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test: fix flaky watch-mode tests with atomic writes #63462

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test: fix flaky watch-mode tests with atomic writes #63462

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19 changes: 15 additions & 4 deletions test/sequential/test-watch-mode-worker.mjs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ import path from 'node:path';
import { execPath } from 'node:process';
import { describe, it } from 'node:test';
import { spawn } from 'node:child_process';
import { writeFileSync, readFileSync } from 'node:fs';
import { writeFileSync, readFileSync, renameSync, unlinkSync } from 'node:fs';
import { inspect } from 'node:util';
import { pathToFileURL } from 'node:url';
import { createInterface } from 'node:readline';
Expand All @@ -14,9 +14,20 @@ if (common.isIBMi)
common.skip('IBMi does not support `fs.watch()`');

function restart(file, content = readFileSync(file)) {
writeFileSync(file, content);
const timer = setInterval(() => writeFileSync(file, content), common.platformTimeout(250));
return () => clearInterval(timer);
// Use atomic writes to avoid flakiness: write to a temp file, then rename.
// writeFileSync is not atomic (it truncates the file before writing),
// which can cause the ESM loader to read an empty/partial file.
const tmpFile = file + '.tmp';
const write = () => {
writeFileSync(tmpFile, content);
renameSync(tmpFile, file);
};
write();
const timer = setInterval(write, common.platformTimeout(2500));
return () => {
clearInterval(timer);
try { unlinkSync(tmpFile); } catch { /* best-effort cleanup */ }
};
}

let tmpFiles = 0;
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20 changes: 15 additions & 5 deletions test/sequential/test-watch-mode.mjs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ import path from 'node:path';
import { execPath } from 'node:process';
import { describe, it } from 'node:test';
import { spawn } from 'node:child_process';
import { writeFileSync, readFileSync, mkdirSync } from 'node:fs';
import { writeFileSync, readFileSync, mkdirSync, renameSync, unlinkSync } from 'node:fs';
import { inspect } from 'node:util';
import { pathToFileURL } from 'node:url';
import { once } from 'node:events';
Expand All @@ -17,10 +17,20 @@ if (common.isIBMi)
const supportsRecursive = common.isMacOS || common.isWindows;

function restart(file, content = readFileSync(file)) {
// To avoid flakiness, we save the file repeatedly until test is done
writeFileSync(file, content);
const timer = setInterval(() => writeFileSync(file, content), common.platformTimeout(2500));
return () => clearInterval(timer);
// Use atomic writes to avoid flakiness: write to a temp file, then rename.
// writeFileSync is not atomic (it truncates the file before writing),
// which can cause the ESM loader to read an empty/partial file.
const tmpFile = file + '.tmp';
const write = () => {
writeFileSync(tmpFile, content);
renameSync(tmpFile, file);
};
write();
const timer = setInterval(write, common.platformTimeout(2500));
return () => {
clearInterval(timer);
try { unlinkSync(tmpFile); } catch { /* best-effort cleanup */ }
};
}

let tmpFiles = 0;
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