diff --git a/packages/rstack/tests/cli/fmt/cache.test.ts b/packages/rstack/tests/cli/fmt/cache.test.ts
new file mode 100644
index 00000000..15e51dea
--- /dev/null
+++ b/packages/rstack/tests/cli/fmt/cache.test.ts
@@ -0,0 +1,132 @@
+import { expect, test } from 'rstack/test';
+import { expectWriteSummary, normalizeDuration, setupFmtTest } from './helpers.ts';
+
+const { projectFileExists, readProjectFile, resolveProjectPath, runFmt, writeProjectFile } =
+  setupFmtTest();
+
+test.each([
+  ['write', []],
+  ['check', ['--check']],
+  ['list-different', ['--list-different']],
+] as const)('uses the default cache in %s mode', (_, args) => {
+  writeProjectFile('index.ts', 'const value = 1;\n');
+  writeProjectFile('.rstack/cache/fmt-v1.json', 'legacy');
+
+  const result = runFmt([...args, 'index.ts']);
+
+  expect(result.status).toBe(0);
+  expect(readProjectFile('.rstack/cache/.gitignore')).toBe('*\n');
+  expect(JSON.parse(readProjectFile('.rstack/cache/fmt/v1.json'))).toMatchObject({
+    version: 1,
+    files: {
+      'index.ts': [expect.any(String), expect.any(String), 'clean'],
+    },
+  });
+  expect(readProjectFile('.rstack/cache/fmt-v1.json')).toBe('legacy');
+});
+
+test('--no-cache bypasses cache reads and writes', () => {
+  writeProjectFile('index.ts', 'const value=1');
+  writeProjectFile('custom-cache/v1.json', '{"value":true}');
+
+  const first = runFmt([
+    '--no-cache',
+    '--cache-location',
+    'custom-cache',
+    'index.ts',
+    'custom-cache/v1.json',
+  ]);
+
+  expect(first.status).toBe(0);
+  expect(readProjectFile('custom-cache/v1.json')).toBe('{ "value": true }\n');
+  expect(projectFileExists('.rstack')).toBe(false);
+
+  writeProjectFile('.rstack/cache/fmt-v1.json', 'stale');
+  writeProjectFile('index.ts', 'const value=2');
+  const second = runFmt(['--no-cache', 'index.ts']);
+
+  expect(second.status).toBe(0);
+  expect(readProjectFile('index.ts')).toBe('const value = 2;\n');
+  expect(readProjectFile('.rstack/cache/fmt-v1.json')).toBe('stale');
+  expect(projectFileExists('.rstack/cache/.gitignore')).toBe(false);
+});
+
+test.each(['relative', 'absolute'] as const)('uses a %s custom cache location', (kind) => {
+  const cacheLocation = kind === 'relative' ? 'custom-cache' : resolveProjectPath('custom-cache');
+  writeProjectFile('index.ts', 'const value = 1;\n');
+
+  const result = runFmt(['--cache-location', cacheLocation, 'index.ts']);
+
+  expect(result.status).toBe(0);
+  expect(JSON.parse(readProjectFile('custom-cache/v1.json'))).toMatchObject({
+    version: 1,
+    files: {
+      'index.ts': [expect.any(String), expect.any(String), 'clean'],
+    },
+  });
+  expect(projectFileExists('custom-cache/.gitignore')).toBe(false);
+  expect(projectFileExists('.rstack')).toBe(false);
+});
+
+test.each(['.', '..'])('rejects a custom cache location at %s', (cacheLocation) => {
+  const result = runFmt(['--cache-location', cacheLocation, '.']);
+
+  expect(result.status).toBe(2);
+  expect(result.stdout).toBe('');
+  expect(result.stderr).toContain(
+    'The --cache-location directory cannot be the current working directory or an ancestor.',
+  );
+});
+
+test('excludes the custom cache directory from formatting', () => {
+  const cacheLocation = 'custom-cache';
+  writeProjectFile('index.ts', 'const value = 1;\n');
+  writeProjectFile('custom-cache/nested/ignored.ts', 'const value=2');
+  expect(runFmt(['--cache-location', cacheLocation, 'index.ts']).status).toBe(0);
+
+  const result = runFmt(['--cache-location', cacheLocation, '.']);
+
+  expect(result.status).toBe(0);
+  expectWriteSummary(result.stdout, 2, 0);
+  expect(readProjectFile('custom-cache/nested/ignored.ts')).toBe('const value=2');
+});
+
+test('uses an explicit config root cache from a subdirectory', () => {
+  const appPath = resolveProjectPath('packages/app');
+  writeProjectFile('packages/app/index.ts', 'const value=1');
+
+  const result = runFmt(['index.ts', '--config', '../../rstack.config.ts'], appPath);
+
+  expect(result.status).toBe(0);
+  expect(readProjectFile('packages/app/index.ts')).toBe('const value = 1;\n');
+  expect(projectFileExists('.rstack/cache/fmt/v1.json')).toBe(true);
+  expect(projectFileExists('packages/app/.rstack')).toBe(false);
+  expect(JSON.parse(readProjectFile('.rstack/cache/fmt/v1.json'))).toMatchObject({
+    files: {
+      'packages/app/index.ts': [expect.any(String), expect.any(String), 'clean'],
+    },
+  });
+});
+
+test('recovers from a corrupted cache', () => {
+  writeProjectFile('index.ts', 'const value = 1;\n');
+  const first = runFmt(['--check', 'index.ts']);
+  writeProjectFile('.rstack/cache/fmt/v1.json', '{');
+
+  const second = runFmt(['--check', 'index.ts']);
+
+  expect(second.status).toBe(0);
+  expect(normalizeDuration(second.stdout)).toBe(normalizeDuration(first.stdout));
+  expect(second.stderr).toBe(first.stderr);
+  expect(JSON.parse(readProjectFile('.rstack/cache/fmt/v1.json'))).toMatchObject({ version: 1 });
+});
+
+test('formats without a writable cache directory', () => {
+  writeProjectFile('.rstack', 'not a directory');
+  writeProjectFile('index.ts', 'const value=1');
+
+  const result = runFmt(['index.ts']);
+
+  expect(result.status).toBe(0);
+  expect(readProjectFile('index.ts')).toBe('const value = 1;\n');
+});
diff --git a/packages/rstack/tests/cli/fmt/config.test.ts b/packages/rstack/tests/cli/fmt/config.test.ts
new file mode 100644
index 00000000..d5947aae
--- /dev/null
+++ b/packages/rstack/tests/cli/fmt/config.test.ts
@@ -0,0 +1,238 @@
+import { expect, test } from 'rstack/test';
+import {
+  expectWriteSummary,
+  packageJsonSource,
+  setupFmtTest,
+  sortedPackageJson,
+} from './helpers.ts';
+
+const { readProjectFile, runFmt, writeFixturePlugin, writeProjectFile } = setupFmtTest();
+
+test('does not sort package.json by default', () => {
+  writeProjectFile('package.json', packageJsonSource);
+
+  const result = runFmt(['package.json']);
+
+  expect(result.status).toBe(0);
+  expect(readProjectFile('package.json')).toContain(
+    '"dependencies": {\n    "z": "1.0.0",\n    "a": "1.0.0"',
+  );
+});
+
+test('sorts package.json with workers', () => {
+  writeProjectFile(
+    'rstack.config.ts',
+    `import { define } from 'rstack';
+
+define.fmt({ sortPackageJson: true });
+`,
+  );
+  writeProjectFile('package.json', packageJsonSource);
+  writeProjectFile('packages/example/package.json', packageJsonSource);
+
+  const result = runFmt(['package.json', 'packages/example/package.json']);
+
+  expect(result.status).toBe(0);
+  expect(result.stderr).toBe('');
+  expect(readProjectFile('package.json')).toBe(sortedPackageJson);
+  expect(readProjectFile('packages/example/package.json')).toBe(sortedPackageJson);
+});
+
+test('supports configuring the worker count', () => {
+  writeProjectFile('first.ts', 'const first="first"');
+  writeProjectFile('second.ts', 'const second="second"');
+
+  const result = runFmt(['--parallel-workers', '1', 'first.ts', 'second.ts']);
+
+  expect(result.status).toBe(0);
+  expectWriteSummary(result.stdout, 2, 2);
+  expect(result.stderr).toBe('');
+  expect(readProjectFile('first.ts')).toBe('const first = "first";\n');
+  expect(readProjectFile('second.ts')).toBe('const second = "second";\n');
+});
+
+test('does not load Prettier config or ignore files', () => {
+  writeProjectFile('.prettierrc.json', '{ "singleQuote": true, "semi": false }\n');
+  writeProjectFile('.prettierignore', 'index.ts\n');
+  writeProjectFile('.editorconfig', 'root = true\n\n[*]\nindent_style = space\nindent_size = 8\n');
+  writeProjectFile('index.ts', "function getMessage(){\n        return 'hello'\n}");
+
+  const result = runFmt(['index.ts']);
+
+  expect(result.status).toBe(0);
+  expectWriteSummary(result.stdout, 1, 1);
+  expect(result.stderr).toBe('');
+  expect(readProjectFile('index.ts')).toBe('function getMessage() {\n  return "hello";\n}\n');
+});
+
+test('applies repeated ignore paths', () => {
+  writeProjectFile('.prettierignore', 'src/ignored-by-root.ts\n');
+  writeProjectFile('config/extra.ignore', '../src/ignored-by-extra.ts\n');
+  writeProjectFile('src/ignored-by-root.ts', 'const root="ignored"');
+  writeProjectFile('src/ignored-by-extra.ts', 'const extra="ignored"');
+  writeProjectFile('src/index.ts', 'const index="formatted"');
+
+  const result = runFmt([
+    '--ignore-path',
+    '.prettierignore',
+    '--ignore-path=config/extra.ignore',
+    'src/ignored-by-root.ts',
+    'src/ignored-by-extra.ts',
+    'src/index.ts',
+  ]);
+
+  expect(result.status).toBe(0);
+  expectWriteSummary(result.stdout, 1, 1);
+  expect(result.stderr).toBe('');
+  expect(readProjectFile('src/ignored-by-root.ts')).toBe('const root="ignored"');
+  expect(readProjectFile('src/ignored-by-extra.ts')).toBe('const extra="ignored"');
+  expect(readProjectFile('src/index.ts')).toBe('const index = "formatted";\n');
+});
+
+test('returns exit code 2 for an unreadable ignore path', () => {
+  writeProjectFile('index.ts', 'const value=true');
+
+  const result = runFmt(['--ignore-path', 'missing.ignore', 'index.ts']);
+
+  expect(result.status).toBe(2);
+  expect(result.stdout).toBe('');
+  expect(result.stderr).toContain('Failed to read ignore file "missing.ignore".');
+  expect(readProjectFile('index.ts')).toBe('const value=true');
+});
+
+test('applies define.fmt options, overrides, ignore patterns, and globs', () => {
+  writeProjectFile(
+    'rstack.config.ts',
+    `import { define } from 'rstack';
+
+define.fmt({
+  singleQuote: true,
+  ignorePatterns: ['src/ignored.ts'],
+  overrides: [
+    {
+      files: '*.test.ts',
+      options: {
+        semi: false,
+      },
+    },
+  ],
+});
+`,
+  );
+  writeProjectFile('src/index.ts', 'const message="hello"');
+  writeProjectFile('src/index.test.ts', 'const test="test"');
+  writeProjectFile('src/ignored.ts', 'const ignored="ignored"');
+  writeProjectFile('src/index.js', 'const javascript="untouched"');
+
+  const result = runFmt(['--write', 'src/**/*.ts']);
+
+  expect(result.status).toBe(0);
+  expectWriteSummary(result.stdout, 2, 2);
+  expect(result.stderr).toBe('');
+  expect(readProjectFile('src/index.ts')).toBe("const message = 'hello';\n");
+  expect(readProjectFile('src/index.test.ts')).toBe("const test = 'test'\n");
+  expect(readProjectFile('src/ignored.ts')).toBe('const ignored="ignored"');
+  expect(readProjectFile('src/index.js')).toBe('const javascript="untouched"');
+});
+
+test('uses an explicit Rstack config', () => {
+  writeProjectFile(
+    'custom.config.ts',
+    `import { define } from 'rstack';
+
+define.fmt({
+  singleQuote: true,
+});
+`,
+  );
+  writeProjectFile('index.ts', 'const message="hello"');
+
+  const result = runFmt(['index.ts', '--config', 'custom.config.ts']);
+
+  expect(result.status).toBe(0);
+  expectWriteSummary(result.stdout, 1, 1);
+  expect(result.stderr).toBe('');
+  expect(readProjectFile('index.ts')).toBe("const message = 'hello';\n");
+});
+
+test('returns exit code 2 for config errors', () => {
+  writeProjectFile('rstack.config.ts', 'throw new Error("invalid fmt config");\n');
+
+  const result = runFmt(['index.ts']);
+
+  expect(result.status).toBe(2);
+  expect(result.stdout).toBe('');
+  expect(result.stderr).toContain('invalid fmt config');
+});
+
+test('formats with a project-local plugin in workers', () => {
+  writeProjectFile(
+    'rstack.config.ts',
+    `import { define } from 'rstack';
+
+define.fmt({
+  plugins: ['prettier-plugin-fixture'],
+});
+`,
+  );
+  writeFixturePlugin();
+  writeProjectFile('first.fixture', '{"first":true}');
+  writeProjectFile('second.fixture', '{"second":true}');
+
+  const result = runFmt(['*.fixture']);
+
+  expect(result.status).toBe(0);
+  expectWriteSummary(result.stdout, 2, 2);
+  expect(result.stderr).toBe('');
+  expect(readProjectFile('first.fixture')).toBe('{ "first": true }\n');
+  expect(readProjectFile('second.fixture')).toBe('{ "second": true }\n');
+});
+
+test('formats mixed plugin overrides in workers', () => {
+  writeProjectFile(
+    'rstack.config.ts',
+    `import { define } from 'rstack';
+
+define.fmt({
+  overrides: [
+    {
+      files: '*.fixture',
+      options: { plugins: ['prettier-plugin-fixture'] },
+    },
+  ],
+});
+`,
+  );
+  writeFixturePlugin();
+  writeProjectFile('data.fixture', '{"value":true}');
+  writeProjectFile('index.ts', 'const value=true');
+
+  const result = runFmt(['data.fixture', 'index.ts']);
+
+  expect(result.status).toBe(0);
+  expectWriteSummary(result.stdout, 2, 2);
+  expect(result.stderr).toBe('');
+  expect(readProjectFile('data.fixture')).toBe('{ "value": true }\n');
+  expect(readProjectFile('index.ts')).toBe('const value = true;\n');
+});
+
+test('returns exit code 2 for imported plugin objects', () => {
+  writeProjectFile(
+    'rstack.config.ts',
+    `import { define } from 'rstack';
+
+define.fmt({
+  plugins: [{ languages: [] }],
+});
+`,
+  );
+  writeProjectFile('index.ts', 'const value=true');
+
+  const result = runFmt(['index.ts']);
+
+  expect(result.status).toBe(2);
+  expect(result.stdout).toBe('');
+  expect(result.stderr).toContain(
+    'Prettier plugin objects are not supported. Use a package name, path, or URL instead.',
+  );
+});
diff --git a/packages/rstack/tests/cli/fmt/files.test.ts b/packages/rstack/tests/cli/fmt/files.test.ts
new file mode 100644
index 00000000..5849356e
--- /dev/null
+++ b/packages/rstack/tests/cli/fmt/files.test.ts
@@ -0,0 +1,155 @@
+import { expect, test } from 'rstack/test';
+import { expectWriteSummary, normalizeDuration, setupFmtTest } from './helpers.ts';
+
+const { readProjectFile, runCLI, runFmt, writeProjectFile } = setupFmtTest();
+
+test('displays fmt help without loading config', () => {
+  writeProjectFile('rstack.config.ts', 'throw new Error("must not load");\n');
+
+  const topLevel = runCLI(['--help']);
+  const fmt = runFmt(['--help']);
+
+  expect(topLevel.status).toBe(0);
+  expect(topLevel.stdout).toContain('fmt, format  Format code');
+  expect(fmt.status).toBe(0);
+  expect(fmt.stdout).toContain('Usage:\n  $ rs fmt [options] [files/globs...]');
+  expect(fmt.stderr).toBe('');
+});
+
+test('supports format as an alias for fmt', () => {
+  writeProjectFile('index.ts', 'const message="hello"');
+
+  const result = runCLI(['format', 'index.ts']);
+
+  expect(result.status).toBe(0);
+  expectWriteSummary(result.stdout, 1, 1);
+  expect(result.stderr).toBe('');
+  expect(readProjectFile('index.ts')).toBe('const message = "hello";\n');
+});
+
+test('returns exit code 2 for invalid arguments', () => {
+  const result = runFmt(['--write', '--check']);
+
+  expect(result.status).toBe(2);
+  expect(result.stdout).toBe('');
+  expect(result.stderr).toContain(
+    'The --write, --check, and --list-different options cannot be used together.',
+  );
+});
+
+test('returns exit code 2 for unknown options', () => {
+  const result = runFmt(['--bogus']);
+
+  expect(result.status).toBe(2);
+  expect(result.stdout).toBe('');
+  expect(result.stderr).toContain('--bogus');
+});
+
+test('formats the current directory with Prettier defaults', () => {
+  writeProjectFile('index.ts', 'const message="hello"');
+
+  const result = runFmt();
+
+  expect(result.status).toBe(0);
+  expectWriteSummary(result.stdout, 2, 1);
+  expect(result.stderr).toBe('');
+  expect(readProjectFile('index.ts')).toBe('const message = "hello";\n');
+});
+
+test('accepts -w as an alias for --write', () => {
+  writeProjectFile('index.ts', 'const message="hello"');
+
+  const result = runFmt(['-w', 'index.ts']);
+
+  expect(result.status).toBe(0);
+  expectWriteSummary(result.stdout, 1, 1);
+  expect(result.stderr).toBe('');
+  expect(readProjectFile('index.ts')).toBe('const message = "hello";\n');
+});
+
+test('formats files in node_modules with --with-node-modules', () => {
+  const source = 'const message="hello"';
+  writeProjectFile('node_modules/example/index.ts', source);
+
+  const skipped = runFmt(['node_modules/example']);
+  expect(skipped.status).toBe(2);
+  expect(readProjectFile('node_modules/example/index.ts')).toBe(source);
+
+  const result = runFmt(['--with-node-modules', 'node_modules/example']);
+  expect(result.status).toBe(0);
+  expectWriteSummary(result.stdout, 1, 1);
+  expect(result.stderr).toBe('');
+  expect(readProjectFile('node_modules/example/index.ts')).toBe('const message = "hello";\n');
+});
+
+test('summarizes write mode when no files change', () => {
+  writeProjectFile('index.ts', 'const message = "hello";\n');
+
+  const result = runFmt(['index.ts']);
+
+  expect(result.status).toBe(0);
+  expectWriteSummary(result.stdout, 1, 0);
+  expect(result.stderr).toBe('');
+});
+
+test('checks formatting without writing files', () => {
+  const source = 'const message="hello"';
+  writeProjectFile('index.ts', source);
+
+  const result = runFmt(['--check', 'index.ts']);
+
+  expect(result.status).toBe(1);
+  expect(normalizeDuration(result.stdout)).toBe(
+    'start   Checking formatting...\ninfo    Checked 1 file in <duration>.\n',
+  );
+  expect(result.stderr).toContain('error   index.ts');
+  expect(normalizeDuration(result.stderr)).toContain(
+    'error   Formatting issues found in 1 file. Run without --check to fix.',
+  );
+  expect(readProjectFile('index.ts')).toBe(source);
+
+  writeProjectFile('index.ts', 'const message = "hello";\n');
+  const formattedResult = runFmt(['--check', 'index.ts']);
+
+  expect(formattedResult.status).toBe(0);
+  expect(normalizeDuration(formattedResult.stdout)).toBe(
+    'start   Checking formatting...\nsuccess Checked 1 file in <duration>. No issues found.\n',
+  );
+  expect(formattedResult.stderr).toBe('');
+});
+
+test.each(['-l', '--list-different'])('lists only paths that differ with %s', (option) => {
+  const source = 'const message="hello"';
+  writeProjectFile('src/index.ts', source);
+  writeProjectFile('src/formatted.ts', 'const formatted = true;\n');
+
+  const result = runFmt([option, 'src/*.ts']);
+
+  expect(result.status).toBe(1);
+  expect(result.stdout).toBe('src/index.ts\n');
+  expect(result.stderr).toBe('');
+  expect(readProjectFile('src/index.ts')).toBe(source);
+});
+
+test('returns exit code 2 for formatting errors', () => {
+  writeProjectFile('index.ts', 'const value = ;');
+
+  const result = runFmt(['index.ts']);
+
+  expect(result.status).toBe(2);
+  expect(result.stdout).toBe('');
+  expect(result.stderr).toContain('error   index.ts: SyntaxError:');
+});
+
+test('reports partial writes when formatting fails', () => {
+  writeProjectFile('valid.ts', 'const value=true');
+  writeProjectFile('invalid.ts', 'const invalid = ;');
+
+  const result = runFmt(['valid.ts', 'invalid.ts']);
+
+  expect(result.status).toBe(2);
+  expect(normalizeDuration(result.stdout)).toBe('info    Formatted 1 of 2 files in <duration>.\n');
+  expect(result.stderr).toContain('error   invalid.ts: SyntaxError:');
+  expect(readProjectFile('valid.ts')).toBe('const value = true;\n');
+  expect(readProjectFile('invalid.ts')).toBe('const invalid = ;');
+});
diff --git a/packages/rstack/tests/cli/fmt/helpers.ts b/packages/rstack/tests/cli/fmt/helpers.ts
new file mode 100644
index 00000000..d441a2fe
--- /dev/null
+++ b/packages/rstack/tests/cli/fmt/helpers.ts
@@ -0,0 +1,108 @@
+import { type SpawnSyncReturns, spawnSync } from 'node:child_process';
+import { existsSync, mkdirSync, mkdtempSync, readFileSync, rmSync, writeFileSync } from 'node:fs';
+import path from 'node:path';
+import { afterEach, beforeEach, expect } from 'rstack/test';
+import { RSTACK_BIN_PATH } from '#test-helpers';
+
+export const packageJsonSource =
+  '{"dependencies":{"z":"1.0.0","a":"1.0.0"},"type":"module","version":"1.0.0","name":"fixture"}';
+export const sortedPackageJson =
+  '{\n  "name": "fixture",\n  "version": "1.0.0",\n  "type": "module",\n  "dependencies": {\n    "a": "1.0.0",\n    "z": "1.0.0"\n  }\n}\n';
+
+type RunCLI = (args: string[], input?: string, cwd?: string) => SpawnSyncReturns<string>;
+
+type FmtTestHarness = {
+  projectFileExists: (filePath: string) => boolean;
+  readProjectFile: (filePath: string) => string;
+  resolveProjectPath: (filePath: string) => string;
+  runCLI: RunCLI;
+  runFmt: (args?: string[], cwd?: string) => SpawnSyncReturns<string>;
+  runFmtStdin: (args: string[], input: string) => SpawnSyncReturns<string>;
+  writeFixturePlugin: () => void;
+  writeProjectFile: (filePath: string, content: string) => void;
+};
+
+export const normalizeDuration = (output: string): string =>
+  output.replace(/\d+m(?: \d+(?:\.\d+)?s)?|\d+(?:\.\d+)?s/g, '<duration>');
+
+export const expectWriteSummary = (
+  output: string,
+  matchedFileCount: number,
+  writtenCount: number,
+): void => {
+  const files = matchedFileCount === 1 ? 'file' : 'files';
+  const message = writtenCount
+    ? `Formatted ${writtenCount} of ${matchedFileCount} ${files} in <duration>.`
+    : `Checked ${matchedFileCount} ${files} in <duration>. No changes needed.`;
+  expect(normalizeDuration(output)).toBe(`success ${message}\n`);
+};
+
+export const setupFmtTest = (): FmtTestHarness => {
+  let projectPath: string;
+
+  const resolveProjectPath = (filePath: string): string => path.join(projectPath, filePath);
+
+  const projectFileExists = (filePath: string): boolean => existsSync(resolveProjectPath(filePath));
+
+  const writeProjectFile = (filePath: string, content: string): void => {
+    const absolutePath = resolveProjectPath(filePath);
+    mkdirSync(path.dirname(absolutePath), { recursive: true });
+    writeFileSync(absolutePath, content);
+  };
+
+  const readProjectFile = (filePath: string): string =>
+    readFileSync(resolveProjectPath(filePath), 'utf8');
+
+  const writeFixturePlugin = (): void => {
+    writeProjectFile(
+      'node_modules/prettier-plugin-fixture/package.json',
+      JSON.stringify({ name: 'prettier-plugin-fixture', exports: './index.mjs' }),
+    );
+    writeProjectFile(
+      'node_modules/prettier-plugin-fixture/index.mjs',
+      `export default {
+  languages: [{ name: 'Fixture JSON', parsers: ['json'], extensions: ['.fixture'] }],
+};
+`,
+    );
+  };
+
+  const runCLI: RunCLI = (args, input, cwd = projectPath) => {
+    const env: NodeJS.ProcessEnv = { ...process.env, NO_COLOR: '1' };
+    delete env.FORCE_COLOR;
+
+    return spawnSync(process.execPath, [RSTACK_BIN_PATH, ...args], {
+      cwd,
+      encoding: 'utf8',
+      env,
+      input,
+    });
+  };
+
+  const runFmt = (args: string[] = [], cwd = projectPath) =>
+    runCLI(['fmt', ...args], undefined, cwd);
+
+  const runFmtStdin = (args: string[], input: string) => runCLI(['fmt', ...args], input);
+
+  beforeEach(() => {
+    projectPath = mkdtempSync(path.join(import.meta.dirname, 'test-temp-fmt-'));
+    // Prevent repository-level ignore rules from affecting the fixture.
+    mkdirSync(path.join(projectPath, '.git'));
+    writeProjectFile('rstack.config.ts', 'export {};\n');
+  });
+
+  afterEach(() => {
+    rmSync(projectPath, { force: true, recursive: true });
+  });
+
+  return {
+    projectFileExists,
+    readProjectFile,
+    resolveProjectPath,
+    runCLI,
+    runFmt,
+    runFmtStdin,
+    writeFixturePlugin,
+    writeProjectFile,
+  };
+};
diff --git a/packages/rstack/tests/cli/fmt/index.test.ts b/packages/rstack/tests/cli/fmt/index.test.ts
deleted file mode 100644
index 289789a7..00000000
--- a/packages/rstack/tests/cli/fmt/index.test.ts
+++ /dev/null
@@ -1,838 +0,0 @@
-import { spawnSync } from 'node:child_process';
-import { existsSync, mkdirSync, mkdtempSync, readFileSync, rmSync, writeFileSync } from 'node:fs';
-import path from 'node:path';
-import { afterEach, beforeEach, expect, test } from 'rstack/test';
-import { RSTACK_BIN_PATH } from '#test-helpers';
-
-let projectPath: string;
-const packageJsonSource =
-  '{"dependencies":{"z":"1.0.0","a":"1.0.0"},"type":"module","version":"1.0.0","name":"fixture"}';
-const sortedPackageJson =
-  '{\n  "name": "fixture",\n  "version": "1.0.0",\n  "type": "module",\n  "dependencies": {\n    "a": "1.0.0",\n    "z": "1.0.0"\n  }\n}\n';
-
-const writeProjectFile = (filePath: string, content: string): void => {
-  const absolutePath = path.join(projectPath, filePath);
-  mkdirSync(path.dirname(absolutePath), { recursive: true });
-  writeFileSync(absolutePath, content);
-};
-
-const readProjectFile = (filePath: string): string =>
-  readFileSync(path.join(projectPath, filePath), 'utf8');
-
-const writeFixturePlugin = (): void => {
-  writeProjectFile(
-    'node_modules/prettier-plugin-fixture/package.json',
-    JSON.stringify({ name: 'prettier-plugin-fixture', exports: './index.mjs' }),
-  );
-  writeProjectFile(
-    'node_modules/prettier-plugin-fixture/index.mjs',
-    `export default {
-  languages: [{ name: 'Fixture JSON', parsers: ['json'], extensions: ['.fixture'] }],
-};
-`,
-  );
-};
-
-const runCLI = (args: string[], input?: string, cwd = projectPath) => {
-  const env: NodeJS.ProcessEnv = { ...process.env, NO_COLOR: '1' };
-  delete env.FORCE_COLOR;
-
-  return spawnSync(process.execPath, [RSTACK_BIN_PATH, ...args], {
-    cwd,
-    encoding: 'utf8',
-    env,
-    input,
-  });
-};
-
-const runFmt = (args: string[] = [], cwd = projectPath) => runCLI(['fmt', ...args], undefined, cwd);
-
-const runFmtStdin = (args: string[], input: string) => runCLI(['fmt', ...args], input);
-
-const normalizeDuration = (output: string): string =>
-  output.replace(/\d+m(?: \d+(?:\.\d+)?s)?|\d+(?:\.\d+)?s/g, '<duration>');
-
-const expectWriteSummary = (
-  output: string,
-  matchedFileCount: number,
-  writtenCount: number,
-): void => {
-  const files = matchedFileCount === 1 ? 'file' : 'files';
-  const message = writtenCount
-    ? `Formatted ${writtenCount} of ${matchedFileCount} ${files} in <duration>.`
-    : `Checked ${matchedFileCount} ${files} in <duration>. No changes needed.`;
-  expect(normalizeDuration(output)).toBe(`success ${message}\n`);
-};
-
-beforeEach(() => {
-  projectPath = mkdtempSync(path.join(import.meta.dirname, 'test-temp-fmt-'));
-  // Prevent repository-level ignore rules from affecting the fixture.
-  mkdirSync(path.join(projectPath, '.git'));
-  writeProjectFile('rstack.config.ts', 'export {};\n');
-});
-
-afterEach(() => {
-  rmSync(projectPath, { force: true, recursive: true });
-});
-
-test('displays fmt help without loading config', () => {
-  writeProjectFile('rstack.config.ts', 'throw new Error("must not load");\n');
-
-  const topLevel = runCLI(['--help']);
-  const fmt = runFmt(['--help']);
-
-  expect(topLevel.status).toBe(0);
-  expect(topLevel.stdout).toContain('fmt, format  Format code');
-  expect(fmt.status).toBe(0);
-  expect(fmt.stdout).toContain('Usage:\n  $ rs fmt [options] [files/globs...]');
-  expect(fmt.stderr).toBe('');
-});
-
-test('supports format as an alias for fmt', () => {
-  writeProjectFile('index.ts', 'const message="hello"');
-
-  const result = runCLI(['format', 'index.ts']);
-
-  expect(result.status).toBe(0);
-  expectWriteSummary(result.stdout, 1, 1);
-  expect(result.stderr).toBe('');
-  expect(readProjectFile('index.ts')).toBe('const message = "hello";\n');
-});
-
-test('returns exit code 2 for invalid arguments', () => {
-  const result = runFmt(['--write', '--check']);
-
-  expect(result.status).toBe(2);
-  expect(result.stdout).toBe('');
-  expect(result.stderr).toContain(
-    'The --write, --check, and --list-different options cannot be used together.',
-  );
-});
-
-test('returns exit code 2 for unknown options', () => {
-  const result = runFmt(['--bogus']);
-
-  expect(result.status).toBe(2);
-  expect(result.stdout).toBe('');
-  expect(result.stderr).toContain('--bogus');
-});
-
-test('formats the current directory with Prettier defaults', () => {
-  writeProjectFile('index.ts', 'const message="hello"');
-
-  const result = runFmt();
-
-  expect(result.status).toBe(0);
-  expectWriteSummary(result.stdout, 2, 1);
-  expect(result.stderr).toBe('');
-  expect(readProjectFile('index.ts')).toBe('const message = "hello";\n');
-});
-
-test('accepts -w as an alias for --write', () => {
-  writeProjectFile('index.ts', 'const message="hello"');
-
-  const result = runFmt(['-w', 'index.ts']);
-
-  expect(result.status).toBe(0);
-  expectWriteSummary(result.stdout, 1, 1);
-  expect(result.stderr).toBe('');
-  expect(readProjectFile('index.ts')).toBe('const message = "hello";\n');
-});
-
-test('formats files in node_modules with --with-node-modules', () => {
-  const source = 'const message="hello"';
-  writeProjectFile('node_modules/example/index.ts', source);
-
-  const skipped = runFmt(['node_modules/example']);
-  expect(skipped.status).toBe(2);
-  expect(readProjectFile('node_modules/example/index.ts')).toBe(source);
-
-  const result = runFmt(['--with-node-modules', 'node_modules/example']);
-  expect(result.status).toBe(0);
-  expectWriteSummary(result.stdout, 1, 1);
-  expect(result.stderr).toBe('');
-  expect(readProjectFile('node_modules/example/index.ts')).toBe('const message = "hello";\n');
-});
-
-test('summarizes write mode when no files change', () => {
-  writeProjectFile('index.ts', 'const message = "hello";\n');
-
-  const result = runFmt(['index.ts']);
-
-  expect(result.status).toBe(0);
-  expectWriteSummary(result.stdout, 1, 0);
-  expect(result.stderr).toBe('');
-});
-
-test.each([
-  ['write', []],
-  ['check', ['--check']],
-  ['list-different', ['--list-different']],
-] as const)('uses the default cache in %s mode', (_, args) => {
-  writeProjectFile('index.ts', 'const value = 1;\n');
-  writeProjectFile('.rstack/cache/fmt-v1.json', 'legacy');
-
-  const result = runFmt([...args, 'index.ts']);
-
-  expect(result.status).toBe(0);
-  expect(readProjectFile('.rstack/cache/.gitignore')).toBe('*\n');
-  expect(JSON.parse(readProjectFile('.rstack/cache/fmt/v1.json'))).toMatchObject({
-    version: 1,
-    files: {
-      'index.ts': [expect.any(String), expect.any(String), 'clean'],
-    },
-  });
-  expect(readProjectFile('.rstack/cache/fmt-v1.json')).toBe('legacy');
-});
-
-test('--no-cache bypasses cache reads and writes', () => {
-  writeProjectFile('index.ts', 'const value=1');
-  writeProjectFile('custom-cache/v1.json', '{"value":true}');
-
-  const first = runFmt([
-    '--no-cache',
-    '--cache-location',
-    'custom-cache',
-    'index.ts',
-    'custom-cache/v1.json',
-  ]);
-
-  expect(first.status).toBe(0);
-  expect(readProjectFile('custom-cache/v1.json')).toBe('{ "value": true }\n');
-  expect(existsSync(path.join(projectPath, '.rstack'))).toBe(false);
-
-  writeProjectFile('.rstack/cache/fmt-v1.json', 'stale');
-  writeProjectFile('index.ts', 'const value=2');
-  const second = runFmt(['--no-cache', 'index.ts']);
-
-  expect(second.status).toBe(0);
-  expect(readProjectFile('index.ts')).toBe('const value = 2;\n');
-  expect(readProjectFile('.rstack/cache/fmt-v1.json')).toBe('stale');
-  expect(existsSync(path.join(projectPath, '.rstack/cache/.gitignore'))).toBe(false);
-});
-
-test.each(['relative', 'absolute'] as const)('uses a %s custom cache location', (kind) => {
-  const cacheDir = path.join(projectPath, 'custom-cache');
-  const cacheLocation = kind === 'relative' ? path.relative(projectPath, cacheDir) : cacheDir;
-  const cachePath = path.join(cacheDir, 'v1.json');
-  writeProjectFile('index.ts', 'const value = 1;\n');
-
-  const result = runFmt(['--cache-location', cacheLocation, 'index.ts']);
-
-  expect(result.status).toBe(0);
-  expect(JSON.parse(readFileSync(cachePath, 'utf8'))).toMatchObject({
-    version: 1,
-    files: {
-      'index.ts': [expect.any(String), expect.any(String), 'clean'],
-    },
-  });
-  expect(existsSync(path.join(projectPath, 'custom-cache/.gitignore'))).toBe(false);
-  expect(existsSync(path.join(projectPath, '.rstack'))).toBe(false);
-});
-
-test.each(['.', '..'])('rejects a custom cache location at %s', (cacheLocation) => {
-  const result = runFmt(['--cache-location', cacheLocation, '.']);
-
-  expect(result.status).toBe(2);
-  expect(result.stdout).toBe('');
-  expect(result.stderr).toContain(
-    'The --cache-location directory cannot be the current working directory or an ancestor.',
-  );
-});
-
-test('excludes the custom cache directory from formatting', () => {
-  const cacheLocation = 'custom-cache';
-  writeProjectFile('index.ts', 'const value = 1;\n');
-  writeProjectFile('custom-cache/nested/ignored.ts', 'const value=2');
-  expect(runFmt(['--cache-location', cacheLocation, 'index.ts']).status).toBe(0);
-
-  const result = runFmt(['--cache-location', cacheLocation, '.']);
-
-  expect(result.status).toBe(0);
-  expectWriteSummary(result.stdout, 2, 0);
-  expect(readProjectFile('custom-cache/nested/ignored.ts')).toBe('const value=2');
-});
-
-test('uses an explicit config root cache from a subdirectory', () => {
-  const appPath = path.join(projectPath, 'packages/app');
-  writeProjectFile('packages/app/index.ts', 'const value=1');
-
-  const result = runFmt(['index.ts', '--config', '../../rstack.config.ts'], appPath);
-
-  expect(result.status).toBe(0);
-  expect(readProjectFile('packages/app/index.ts')).toBe('const value = 1;\n');
-  expect(existsSync(path.join(projectPath, '.rstack/cache/fmt/v1.json'))).toBe(true);
-  expect(existsSync(path.join(appPath, '.rstack'))).toBe(false);
-  expect(JSON.parse(readProjectFile('.rstack/cache/fmt/v1.json'))).toMatchObject({
-    files: {
-      'packages/app/index.ts': [expect.any(String), expect.any(String), 'clean'],
-    },
-  });
-});
-
-test('recovers from a corrupted cache', () => {
-  writeProjectFile('index.ts', 'const value = 1;\n');
-  const first = runFmt(['--check', 'index.ts']);
-  writeProjectFile('.rstack/cache/fmt/v1.json', '{');
-
-  const second = runFmt(['--check', 'index.ts']);
-
-  expect(second.status).toBe(0);
-  expect(normalizeDuration(second.stdout)).toBe(normalizeDuration(first.stdout));
-  expect(second.stderr).toBe(first.stderr);
-  expect(JSON.parse(readProjectFile('.rstack/cache/fmt/v1.json'))).toMatchObject({ version: 1 });
-});
-
-test('formats without a writable cache directory', () => {
-  writeProjectFile('.rstack', 'not a directory');
-  writeProjectFile('index.ts', 'const value=1');
-
-  const result = runFmt(['index.ts']);
-
-  expect(result.status).toBe(0);
-  expect(readProjectFile('index.ts')).toBe('const value = 1;\n');
-});
-
-test('does not sort package.json by default', () => {
-  writeProjectFile('package.json', packageJsonSource);
-
-  const result = runFmt(['package.json']);
-
-  expect(result.status).toBe(0);
-  expect(readProjectFile('package.json')).toContain(
-    '"dependencies": {\n    "z": "1.0.0",\n    "a": "1.0.0"',
-  );
-});
-
-test('sorts package.json with workers', () => {
-  writeProjectFile(
-    'rstack.config.ts',
-    `import { define } from 'rstack';
-
-define.fmt({ sortPackageJson: true });
-`,
-  );
-  writeProjectFile('package.json', packageJsonSource);
-  writeProjectFile('packages/example/package.json', packageJsonSource);
-
-  const result = runFmt(['package.json', 'packages/example/package.json']);
-
-  expect(result.status).toBe(0);
-  expect(result.stderr).toBe('');
-  expect(readProjectFile('package.json')).toBe(sortedPackageJson);
-  expect(readProjectFile('packages/example/package.json')).toBe(sortedPackageJson);
-});
-
-test('supports configuring the worker count', () => {
-  writeProjectFile('first.ts', 'const first="first"');
-  writeProjectFile('second.ts', 'const second="second"');
-
-  const result = runFmt(['--parallel-workers', '1', 'first.ts', 'second.ts']);
-
-  expect(result.status).toBe(0);
-  expectWriteSummary(result.stdout, 2, 2);
-  expect(result.stderr).toBe('');
-  expect(readProjectFile('first.ts')).toBe('const first = "first";\n');
-  expect(readProjectFile('second.ts')).toBe('const second = "second";\n');
-});
-
-test('does not load Prettier config or ignore files', () => {
-  writeProjectFile('.prettierrc.json', '{ "singleQuote": true, "semi": false }\n');
-  writeProjectFile('.prettierignore', 'index.ts\n');
-  writeProjectFile('.editorconfig', 'root = true\n\n[*]\nindent_style = space\nindent_size = 8\n');
-  writeProjectFile('index.ts', "function getMessage(){\n        return 'hello'\n}");
-
-  const result = runFmt(['index.ts']);
-
-  expect(result.status).toBe(0);
-  expectWriteSummary(result.stdout, 1, 1);
-  expect(result.stderr).toBe('');
-  expect(readProjectFile('index.ts')).toBe('function getMessage() {\n  return "hello";\n}\n');
-});
-
-test('applies repeated ignore paths', () => {
-  writeProjectFile('.prettierignore', 'src/ignored-by-root.ts\n');
-  writeProjectFile('config/extra.ignore', '../src/ignored-by-extra.ts\n');
-  writeProjectFile('src/ignored-by-root.ts', 'const root="ignored"');
-  writeProjectFile('src/ignored-by-extra.ts', 'const extra="ignored"');
-  writeProjectFile('src/index.ts', 'const index="formatted"');
-
-  const result = runFmt([
-    '--ignore-path',
-    '.prettierignore',
-    '--ignore-path=config/extra.ignore',
-    'src/ignored-by-root.ts',
-    'src/ignored-by-extra.ts',
-    'src/index.ts',
-  ]);
-
-  expect(result.status).toBe(0);
-  expectWriteSummary(result.stdout, 1, 1);
-  expect(result.stderr).toBe('');
-  expect(readProjectFile('src/ignored-by-root.ts')).toBe('const root="ignored"');
-  expect(readProjectFile('src/ignored-by-extra.ts')).toBe('const extra="ignored"');
-  expect(readProjectFile('src/index.ts')).toBe('const index = "formatted";\n');
-});
-
-test('returns exit code 2 for an unreadable ignore path', () => {
-  writeProjectFile('index.ts', 'const value=true');
-
-  const result = runFmt(['--ignore-path', 'missing.ignore', 'index.ts']);
-
-  expect(result.status).toBe(2);
-  expect(result.stdout).toBe('');
-  expect(result.stderr).toContain('Failed to read ignore file "missing.ignore".');
-  expect(readProjectFile('index.ts')).toBe('const value=true');
-});
-
-test('applies define.fmt options, overrides, ignore patterns, and globs', () => {
-  writeProjectFile(
-    'rstack.config.ts',
-    `import { define } from 'rstack';
-
-define.fmt({
-  singleQuote: true,
-  ignorePatterns: ['src/ignored.ts'],
-  overrides: [
-    {
-      files: '*.test.ts',
-      options: {
-        semi: false,
-      },
-    },
-  ],
-});
-`,
-  );
-  writeProjectFile('src/index.ts', 'const message="hello"');
-  writeProjectFile('src/index.test.ts', 'const test="test"');
-  writeProjectFile('src/ignored.ts', 'const ignored="ignored"');
-  writeProjectFile('src/index.js', 'const javascript="untouched"');
-
-  const result = runFmt(['--write', 'src/**/*.ts']);
-
-  expect(result.status).toBe(0);
-  expectWriteSummary(result.stdout, 2, 2);
-  expect(result.stderr).toBe('');
-  expect(readProjectFile('src/index.ts')).toBe("const message = 'hello';\n");
-  expect(readProjectFile('src/index.test.ts')).toBe("const test = 'test'\n");
-  expect(readProjectFile('src/ignored.ts')).toBe('const ignored="ignored"');
-  expect(readProjectFile('src/index.js')).toBe('const javascript="untouched"');
-});
-
-test('uses an explicit Rstack config', () => {
-  writeProjectFile(
-    'custom.config.ts',
-    `import { define } from 'rstack';
-
-define.fmt({
-  singleQuote: true,
-});
-`,
-  );
-  writeProjectFile('index.ts', 'const message="hello"');
-
-  const result = runFmt(['index.ts', '--config', 'custom.config.ts']);
-
-  expect(result.status).toBe(0);
-  expectWriteSummary(result.stdout, 1, 1);
-  expect(result.stderr).toBe('');
-  expect(readProjectFile('index.ts')).toBe("const message = 'hello';\n");
-});
-
-test('checks formatting without writing files', () => {
-  const source = 'const message="hello"';
-  writeProjectFile('index.ts', source);
-
-  const result = runFmt(['--check', 'index.ts']);
-
-  expect(result.status).toBe(1);
-  expect(normalizeDuration(result.stdout)).toBe(
-    'start   Checking formatting...\ninfo    Checked 1 file in <duration>.\n',
-  );
-  expect(result.stderr).toContain('error   index.ts');
-  expect(normalizeDuration(result.stderr)).toContain(
-    'error   Formatting issues found in 1 file. Run without --check to fix.',
-  );
-  expect(readProjectFile('index.ts')).toBe(source);
-
-  writeProjectFile('index.ts', 'const message = "hello";\n');
-  const formattedResult = runFmt(['--check', 'index.ts']);
-
-  expect(formattedResult.status).toBe(0);
-  expect(normalizeDuration(formattedResult.stdout)).toBe(
-    'start   Checking formatting...\nsuccess Checked 1 file in <duration>. No issues found.\n',
-  );
-  expect(formattedResult.stderr).toBe('');
-});
-
-test.each(['-l', '--list-different'])('lists only paths that differ with %s', (option) => {
-  const source = 'const message="hello"';
-  writeProjectFile('src/index.ts', source);
-  writeProjectFile('src/formatted.ts', 'const formatted = true;\n');
-
-  const result = runFmt([option, 'src/*.ts']);
-
-  expect(result.status).toBe(1);
-  expect(result.stdout).toBe('src/index.ts\n');
-  expect(result.stderr).toBe('');
-  expect(readProjectFile('src/index.ts')).toBe(source);
-});
-
-test('returns exit code 2 for config errors', () => {
-  writeProjectFile('rstack.config.ts', 'throw new Error("invalid fmt config");\n');
-
-  const result = runFmt(['index.ts']);
-
-  expect(result.status).toBe(2);
-  expect(result.stdout).toBe('');
-  expect(result.stderr).toContain('invalid fmt config');
-});
-
-test('formats with a project-local plugin in workers', () => {
-  writeProjectFile(
-    'rstack.config.ts',
-    `import { define } from 'rstack';
-
-define.fmt({
-  plugins: ['prettier-plugin-fixture'],
-});
-`,
-  );
-  writeFixturePlugin();
-  writeProjectFile('first.fixture', '{"first":true}');
-  writeProjectFile('second.fixture', '{"second":true}');
-
-  const result = runFmt(['*.fixture']);
-
-  expect(result.status).toBe(0);
-  expectWriteSummary(result.stdout, 2, 2);
-  expect(result.stderr).toBe('');
-  expect(readProjectFile('first.fixture')).toBe('{ "first": true }\n');
-  expect(readProjectFile('second.fixture')).toBe('{ "second": true }\n');
-});
-
-test('formats mixed plugin overrides in workers', () => {
-  writeProjectFile(
-    'rstack.config.ts',
-    `import { define } from 'rstack';
-
-define.fmt({
-  overrides: [
-    {
-      files: '*.fixture',
-      options: { plugins: ['prettier-plugin-fixture'] },
-    },
-  ],
-});
-`,
-  );
-  writeFixturePlugin();
-  writeProjectFile('data.fixture', '{"value":true}');
-  writeProjectFile('index.ts', 'const value=true');
-
-  const result = runFmt(['data.fixture', 'index.ts']);
-
-  expect(result.status).toBe(0);
-  expectWriteSummary(result.stdout, 2, 2);
-  expect(result.stderr).toBe('');
-  expect(readProjectFile('data.fixture')).toBe('{ "value": true }\n');
-  expect(readProjectFile('index.ts')).toBe('const value = true;\n');
-});
-
-test('returns exit code 2 for imported plugin objects', () => {
-  writeProjectFile(
-    'rstack.config.ts',
-    `import { define } from 'rstack';
-
-define.fmt({
-  plugins: [{ languages: [] }],
-});
-`,
-  );
-  writeProjectFile('index.ts', 'const value=true');
-
-  const result = runFmt(['index.ts']);
-
-  expect(result.status).toBe(2);
-  expect(result.stdout).toBe('');
-  expect(result.stderr).toContain(
-    'Prettier plugin objects are not supported. Use a package name, path, or URL instead.',
-  );
-});
-
-test('returns exit code 2 for formatting errors', () => {
-  writeProjectFile('index.ts', 'const value = ;');
-
-  const result = runFmt(['index.ts']);
-
-  expect(result.status).toBe(2);
-  expect(result.stdout).toBe('');
-  expect(result.stderr).toContain('error   index.ts: SyntaxError:');
-});
-
-test('reports partial writes when formatting fails', () => {
-  writeProjectFile('valid.ts', 'const value=true');
-  writeProjectFile('invalid.ts', 'const invalid = ;');
-
-  const result = runFmt(['valid.ts', 'invalid.ts']);
-
-  expect(result.status).toBe(2);
-  expect(normalizeDuration(result.stdout)).toBe('info    Formatted 1 of 2 files in <duration>.\n');
-  expect(result.stderr).toContain('error   invalid.ts: SyntaxError:');
-  expect(readProjectFile('valid.ts')).toBe('const value = true;\n');
-  expect(readProjectFile('invalid.ts')).toBe('const invalid = ;');
-});
-
-test('formats stdin for the given filepath', () => {
-  const result = runFmtStdin(['--stdin-filepath', 'src/index.ts'], 'const message="hello"');
-
-  expect(result.status).toBe(0);
-  expect(result.stdout).toBe('const message = "hello";\n');
-  expect(result.stderr).toBe('');
-  expect(existsSync(path.join(projectPath, '.rstack'))).toBe(false);
-});
-
-test('applies define.fmt options and overrides to stdin', () => {
-  writeProjectFile(
-    'rstack.config.ts',
-    `import { define } from 'rstack';
-
-define.fmt({
-  singleQuote: true,
-  overrides: [
-    {
-      files: '*.test.ts',
-      options: {
-        semi: false,
-      },
-    },
-  ],
-});
-`,
-  );
-
-  const result = runFmtStdin(['--stdin-filepath', 'src/index.test.ts'], 'const test="test"');
-
-  expect(result.status).toBe(0);
-  expect(result.stdout).toBe("const test = 'test'\n");
-  expect(result.stderr).toBe('');
-});
-
-test('sorts package.json from stdin', () => {
-  writeProjectFile(
-    'rstack.config.ts',
-    `import { define } from 'rstack';
-
-define.fmt({ sortPackageJson: true });
-`,
-  );
-
-  const result = runFmtStdin(['--stdin-filepath', 'package.json'], packageJsonSource);
-
-  expect(result.status).toBe(0);
-  expect(result.stdout).toBe(sortedPackageJson);
-  expect(result.stderr).toBe('');
-});
-
-test('echoes ignored stdin paths verbatim', () => {
-  writeProjectFile(
-    'rstack.config.ts',
-    `import { define } from 'rstack';
-
-define.fmt({ ignorePatterns: ['src/ignored.ts'] });
-`,
-  );
-
-  const source = 'const ignored="ignored"';
-  const result = runFmtStdin(['--stdin-filepath', 'src/ignored.ts'], source);
-
-  expect(result.status).toBe(0);
-  expect(result.stdout).toBe(source);
-  expect(result.stderr).toBe('');
-});
-
-test('echoes stdin paths ignored by --ignore-path', () => {
-  writeProjectFile('.prettierignore', 'src/ignored.ts\n');
-
-  const source = 'const ignored="ignored"';
-  const result = runFmtStdin(
-    ['--ignore-path', '.prettierignore', '--stdin-filepath', 'src/ignored.ts'],
-    source,
-  );
-
-  expect(result.status).toBe(0);
-  expect(result.stdout).toBe(source);
-  expect(result.stderr).toBe('');
-});
-
-test('echoes stdin for default ignored lock files', () => {
-  const source = 'lockfileVersion:   "9.0"\n';
-  const result = runFmtStdin(['--stdin-filepath', 'pnpm-lock.yaml'], source);
-
-  expect(result.status).toBe(0);
-  expect(result.stdout).toBe(source);
-  expect(result.stderr).toBe('');
-});
-
-test('returns exit code 2 when no parser can be inferred for stdin', () => {
-  const result = runFmtStdin(['--stdin-filepath', 'data.unknown'], 'value');
-
-  expect(result.status).toBe(2);
-  expect(result.stdout).toBe('');
-  expect(result.stderr).toContain('No parser could be inferred for "data.unknown".');
-});
-
-test('ignores stdin when no parser can be inferred with --ignore-unknown', () => {
-  const result = runFmtStdin(['--stdin-filepath', 'data.unknown', '--ignore-unknown'], 'value');
-
-  expect(result.status).toBe(0);
-  expect(result.stdout).toBe('');
-  expect(result.stderr).toBe('');
-});
-
-test('returns exit code 2 for stdin parse errors', () => {
-  const result = runFmtStdin(['--stdin-filepath', 'index.ts'], 'const value = ;');
-
-  expect(result.status).toBe(2);
-  expect(result.stdout).toBe('');
-  expect(result.stderr).toContain("Unexpected token ';'");
-});
-
-test.each(['--write', '--check', '--list-different'])(
-  'returns exit code 2 for %s with --stdin-filepath',
-  (option) => {
-    const result = runFmtStdin(['--stdin-filepath', 'index.ts', option], 'const value=1');
-
-    expect(result.status).toBe(2);
-    expect(result.stdout).toBe('');
-    expect(result.stderr).toContain(
-      'The --stdin-filepath option cannot be used with --write, --check, or --list-different.',
-    );
-  },
-);
-
-test('returns exit code 2 for file arguments with --stdin-filepath', () => {
-  const result = runFmtStdin(['--stdin-filepath', 'index.ts', 'src/other.ts'], 'const value=1');
-
-  expect(result.status).toBe(2);
-  expect(result.stdout).toBe('');
-  expect(result.stderr).toContain(
-    'The --stdin-filepath option cannot be used with file arguments.',
-  );
-});
-
-test('accepts --parallel-workers with --stdin-filepath', () => {
-  const result = runFmtStdin(
-    ['--stdin-filepath', 'index.ts', '--parallel-workers', '2'],
-    'const value=1',
-  );
-
-  expect(result.status).toBe(0);
-  expect(result.stdout).toBe('const value = 1;\n');
-  expect(result.stderr).toBe('');
-});
-
-test('writes nothing for empty stdin', () => {
-  const result = runFmtStdin(['--stdin-filepath', 'index.ts'], '');
-
-  expect(result.status).toBe(0);
-  expect(result.stdout).toBe('');
-  expect(result.stderr).toBe('');
-});
-
-test('returns exit code 2 when no files match', () => {
-  for (const modeArgs of [[], ['--check'], ['--list-different']]) {
-    const result = runFmt([...modeArgs, 'missing/**/*.ts']);
-
-    expect(result.status).toBe(2);
-    expect(result.stdout).toBe('');
-    expect(result.stderr).toContain(
-      'No supported files matched "missing/**/*.ts", or all matching files were ignored.',
-    );
-    expect(result.stderr).not.toContain('\n    at ');
-  }
-  expect(existsSync(path.join(projectPath, '.rstack'))).toBe(false);
-});
-
-test('allows no files to match with --no-error-on-unmatched-pattern', () => {
-  for (const modeArgs of [[], ['--check'], ['--list-different']]) {
-    const result = runFmt([...modeArgs, '--no-error-on-unmatched-pattern', 'missing/**/*.ts']);
-
-    expect(result.status).toBe(0);
-    expect(result.stdout).toBe('');
-    expect(result.stderr).toBe('');
-  }
-});
-
-test('counts only supported files', () => {
-  writeProjectFile('index.ts', 'const value = 1;\n');
-  writeProjectFile('notes.unknown', 'plain text');
-
-  const result = runFmt(['--check', 'index.ts', 'notes.unknown']);
-
-  expect(result.status).toBe(0);
-  expect(normalizeDuration(result.stdout)).toBe(
-    'start   Checking formatting...\nsuccess Checked 1 file in <duration>. No issues found.\n',
-  );
-  expect(result.stderr).toBe('');
-});
-
-test('returns exit code 2 when all matched files are unsupported', () => {
-  writeProjectFile('notes.unknown', 'plain text');
-
-  for (const modeArgs of [[], ['--check'], ['--list-different']]) {
-    const result = runFmt([...modeArgs, 'notes.unknown']);
-
-    expect(result.status).toBe(2);
-    expect(result.stdout).not.toContain('success');
-    expect(result.stderr).toContain(
-      'No supported files matched "notes.unknown", or all matching files were ignored.',
-    );
-    expect(result.stderr).not.toContain('\n    at ');
-  }
-});
-
-test('ignores unsupported files with --ignore-unknown', () => {
-  writeProjectFile('notes.unknown', 'plain text');
-
-  for (const modeArgs of [[], ['--check'], ['--list-different']]) {
-    const result = runFmt([...modeArgs, '--ignore-unknown', 'notes.unknown']);
-
-    expect(result.status).toBe(0);
-    expect(result.stdout).toBe(
-      modeArgs.includes('--check')
-        ? 'start   Checking formatting...\nsuccess No supported files to check.\n'
-        : '',
-    );
-    expect(result.stderr).toBe('');
-  }
-});
-
-test('supports -u as an alias for --ignore-unknown', () => {
-  writeProjectFile('notes.unknown', 'plain text');
-
-  const result = runFmt(['-u', 'notes.unknown']);
-
-  expect(result.status).toBe(0);
-  expect(result.stdout).toBe('');
-  expect(result.stderr).toBe('');
-});
-
-test('does not treat unmatched patterns as unknown files', () => {
-  const result = runFmt(['--ignore-unknown', 'missing/**/*.unknown']);
-
-  expect(result.status).toBe(2);
-  expect(result.stdout).toBe('');
-  expect(result.stderr).toContain('No supported files matched "missing/**/*.unknown"');
-});
-
-test('does not treat unsupported files as unmatched patterns', () => {
-  writeProjectFile('notes.unknown', 'plain text');
-
-  const result = runFmt(['--no-error-on-unmatched-pattern', 'notes.unknown']);
-
-  expect(result.status).toBe(2);
-  expect(result.stdout).toBe('');
-  expect(result.stderr).toContain('No supported files matched "notes.unknown"');
-});
diff --git a/packages/rstack/tests/cli/fmt/patterns.test.ts b/packages/rstack/tests/cli/fmt/patterns.test.ts
new file mode 100644
index 00000000..0334dde1
--- /dev/null
+++ b/packages/rstack/tests/cli/fmt/patterns.test.ts
@@ -0,0 +1,100 @@
+import { expect, test } from 'rstack/test';
+import { normalizeDuration, setupFmtTest } from './helpers.ts';
+
+const { projectFileExists, runFmt, writeProjectFile } = setupFmtTest();
+
+test('returns exit code 2 when no files match', () => {
+  for (const modeArgs of [[], ['--check'], ['--list-different']]) {
+    const result = runFmt([...modeArgs, 'missing/**/*.ts']);
+
+    expect(result.status).toBe(2);
+    expect(result.stdout).toBe('');
+    expect(result.stderr).toContain(
+      'No supported files matched "missing/**/*.ts", or all matching files were ignored.',
+    );
+    expect(result.stderr).not.toContain('\n    at ');
+  }
+  expect(projectFileExists('.rstack')).toBe(false);
+});
+
+test('allows no files to match with --no-error-on-unmatched-pattern', () => {
+  for (const modeArgs of [[], ['--check'], ['--list-different']]) {
+    const result = runFmt([...modeArgs, '--no-error-on-unmatched-pattern', 'missing/**/*.ts']);
+
+    expect(result.status).toBe(0);
+    expect(result.stdout).toBe('');
+    expect(result.stderr).toBe('');
+  }
+});
+
+test('counts only supported files', () => {
+  writeProjectFile('index.ts', 'const value = 1;\n');
+  writeProjectFile('notes.unknown', 'plain text');
+
+  const result = runFmt(['--check', 'index.ts', 'notes.unknown']);
+
+  expect(result.status).toBe(0);
+  expect(normalizeDuration(result.stdout)).toBe(
+    'start   Checking formatting...\nsuccess Checked 1 file in <duration>. No issues found.\n',
+  );
+  expect(result.stderr).toBe('');
+});
+
+test('returns exit code 2 when all matched files are unsupported', () => {
+  writeProjectFile('notes.unknown', 'plain text');
+
+  for (const modeArgs of [[], ['--check'], ['--list-different']]) {
+    const result = runFmt([...modeArgs, 'notes.unknown']);
+
+    expect(result.status).toBe(2);
+    expect(result.stdout).not.toContain('success');
+    expect(result.stderr).toContain(
+      'No supported files matched "notes.unknown", or all matching files were ignored.',
+    );
+    expect(result.stderr).not.toContain('\n    at ');
+  }
+});
+
+test('ignores unsupported files with --ignore-unknown', () => {
+  writeProjectFile('notes.unknown', 'plain text');
+
+  for (const modeArgs of [[], ['--check'], ['--list-different']]) {
+    const result = runFmt([...modeArgs, '--ignore-unknown', 'notes.unknown']);
+
+    expect(result.status).toBe(0);
+    expect(result.stdout).toBe(
+      modeArgs.includes('--check')
+        ? 'start   Checking formatting...\nsuccess No supported files to check.\n'
+        : '',
+    );
+    expect(result.stderr).toBe('');
+  }
+});
+
+test('supports -u as an alias for --ignore-unknown', () => {
+  writeProjectFile('notes.unknown', 'plain text');
+
+  const result = runFmt(['-u', 'notes.unknown']);
+
+  expect(result.status).toBe(0);
+  expect(result.stdout).toBe('');
+  expect(result.stderr).toBe('');
+});
+
+test('does not treat unmatched patterns as unknown files', () => {
+  const result = runFmt(['--ignore-unknown', 'missing/**/*.unknown']);
+
+  expect(result.status).toBe(2);
+  expect(result.stdout).toBe('');
+  expect(result.stderr).toContain('No supported files matched "missing/**/*.unknown"');
+});
+
+test('does not treat unsupported files as unmatched patterns', () => {
+  writeProjectFile('notes.unknown', 'plain text');
+
+  const result = runFmt(['--no-error-on-unmatched-pattern', 'notes.unknown']);
+
+  expect(result.status).toBe(2);
+  expect(result.stdout).toBe('');
+  expect(result.stderr).toContain('No supported files matched "notes.unknown"');
+});
diff --git a/packages/rstack/tests/cli/fmt/stdin.test.ts b/packages/rstack/tests/cli/fmt/stdin.test.ts
new file mode 100644
index 00000000..21e5a4c5
--- /dev/null
+++ b/packages/rstack/tests/cli/fmt/stdin.test.ts
@@ -0,0 +1,161 @@
+import { expect, test } from 'rstack/test';
+import { packageJsonSource, setupFmtTest, sortedPackageJson } from './helpers.ts';
+
+const { projectFileExists, runFmtStdin, writeProjectFile } = setupFmtTest();
+
+test('formats stdin for the given filepath', () => {
+  const result = runFmtStdin(['--stdin-filepath', 'src/index.ts'], 'const message="hello"');
+
+  expect(result.status).toBe(0);
+  expect(result.stdout).toBe('const message = "hello";\n');
+  expect(result.stderr).toBe('');
+  expect(projectFileExists('.rstack')).toBe(false);
+});
+
+test('applies define.fmt options and overrides to stdin', () => {
+  writeProjectFile(
+    'rstack.config.ts',
+    `import { define } from 'rstack';
+
+define.fmt({
+  singleQuote: true,
+  overrides: [
+    {
+      files: '*.test.ts',
+      options: {
+        semi: false,
+      },
+    },
+  ],
+});
+`,
+  );
+
+  const result = runFmtStdin(['--stdin-filepath', 'src/index.test.ts'], 'const test="test"');
+
+  expect(result.status).toBe(0);
+  expect(result.stdout).toBe("const test = 'test'\n");
+  expect(result.stderr).toBe('');
+});
+
+test('sorts package.json from stdin', () => {
+  writeProjectFile(
+    'rstack.config.ts',
+    `import { define } from 'rstack';
+
+define.fmt({ sortPackageJson: true });
+`,
+  );
+
+  const result = runFmtStdin(['--stdin-filepath', 'package.json'], packageJsonSource);
+
+  expect(result.status).toBe(0);
+  expect(result.stdout).toBe(sortedPackageJson);
+  expect(result.stderr).toBe('');
+});
+
+test('echoes ignored stdin paths verbatim', () => {
+  writeProjectFile(
+    'rstack.config.ts',
+    `import { define } from 'rstack';
+
+define.fmt({ ignorePatterns: ['src/ignored.ts'] });
+`,
+  );
+
+  const source = 'const ignored="ignored"';
+  const result = runFmtStdin(['--stdin-filepath', 'src/ignored.ts'], source);
+
+  expect(result.status).toBe(0);
+  expect(result.stdout).toBe(source);
+  expect(result.stderr).toBe('');
+});
+
+test('echoes stdin paths ignored by --ignore-path', () => {
+  writeProjectFile('.prettierignore', 'src/ignored.ts\n');
+
+  const source = 'const ignored="ignored"';
+  const result = runFmtStdin(
+    ['--ignore-path', '.prettierignore', '--stdin-filepath', 'src/ignored.ts'],
+    source,
+  );
+
+  expect(result.status).toBe(0);
+  expect(result.stdout).toBe(source);
+  expect(result.stderr).toBe('');
+});
+
+test('echoes stdin for default ignored lock files', () => {
+  const source = 'lockfileVersion:   "9.0"\n';
+  const result = runFmtStdin(['--stdin-filepath', 'pnpm-lock.yaml'], source);
+
+  expect(result.status).toBe(0);
+  expect(result.stdout).toBe(source);
+  expect(result.stderr).toBe('');
+});
+
+test('returns exit code 2 when no parser can be inferred for stdin', () => {
+  const result = runFmtStdin(['--stdin-filepath', 'data.unknown'], 'value');
+
+  expect(result.status).toBe(2);
+  expect(result.stdout).toBe('');
+  expect(result.stderr).toContain('No parser could be inferred for "data.unknown".');
+});
+
+test('ignores stdin when no parser can be inferred with --ignore-unknown', () => {
+  const result = runFmtStdin(['--stdin-filepath', 'data.unknown', '--ignore-unknown'], 'value');
+
+  expect(result.status).toBe(0);
+  expect(result.stdout).toBe('');
+  expect(result.stderr).toBe('');
+});
+
+test('returns exit code 2 for stdin parse errors', () => {
+  const result = runFmtStdin(['--stdin-filepath', 'index.ts'], 'const value = ;');
+
+  expect(result.status).toBe(2);
+  expect(result.stdout).toBe('');
+  expect(result.stderr).toContain("Unexpected token ';'");
+});
+
+test.each(['--write', '--check', '--list-different'])(
+  'returns exit code 2 for %s with --stdin-filepath',
+  (option) => {
+    const result = runFmtStdin(['--stdin-filepath', 'index.ts', option], 'const value=1');
+
+    expect(result.status).toBe(2);
+    expect(result.stdout).toBe('');
+    expect(result.stderr).toContain(
+      'The --stdin-filepath option cannot be used with --write, --check, or --list-different.',
+    );
+  },
+);
+
+test('returns exit code 2 for file arguments with --stdin-filepath', () => {
+  const result = runFmtStdin(['--stdin-filepath', 'index.ts', 'src/other.ts'], 'const value=1');
+
+  expect(result.status).toBe(2);
+  expect(result.stdout).toBe('');
+  expect(result.stderr).toContain(
+    'The --stdin-filepath option cannot be used with file arguments.',
+  );
+});
+
+test('accepts --parallel-workers with --stdin-filepath', () => {
+  const result = runFmtStdin(
+    ['--stdin-filepath', 'index.ts', '--parallel-workers', '2'],
+    'const value=1',
+  );
+
+  expect(result.status).toBe(0);
+  expect(result.stdout).toBe('const value = 1;\n');
+  expect(result.stderr).toBe('');
+});
+
+test('writes nothing for empty stdin', () => {
+  const result = runFmtStdin(['--stdin-filepath', 'index.ts'], '');
+
+  expect(result.status).toBe(0);
+  expect(result.stdout).toBe('');
+  expect(result.stderr).toBe('');
+});