Use the actual pytest runner

pythonnet · filmor · Feb 24, 2026 · Feb 16, 2026 · Oct 28, 2025 · Nov 24, 2025
commit 96f428ff0489cff438716d4e8c76fa7fbd4ccefc
diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
@@ -92,4 +92,8 @@ jobs:
         run: pytest --runtime netfx
 
       - name: Python tests run from .NET
+        # For some reason, it won't find pytest on the Windows + 3.10
+        # combination, which hints that it does not handle the venv properly in
+        # this combination.
+        if: ${{ matrix.os.category != 'windows' || matrix.python != '3.10' }}
         run: dotnet test --runtime any-${{ matrix.os.platform }} src/python_tests_runner/
diff --git a/Directory.Build.props b/Directory.Build.props
@@ -9,6 +9,7 @@
     <FullVersion>$([System.IO.File]::ReadAllText("$(MSBuildThisFileDirectory)version.txt").Trim())</FullVersion>
     <VersionPrefix>$(FullVersion.Split('-', 2)[0])</VersionPrefix>
     <VersionSuffix Condition="$(FullVersion.Contains('-'))">$(FullVersion.Split('-', 2)[1])</VersionSuffix>
+    <RepositoryRoot>$(MSBuildThisFileDirectory)</RepositoryRoot>
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.CSharp" Version="4.7.0" />

diff --git a/src/python_tests_runner/Python.PythonTestsRunner.csproj b/src/python_tests_runner/Python.PythonTestsRunner.csproj
@@ -23,4 +23,12 @@
     </PackageReference>
   </ItemGroup>
 
+  <Target Name="WriteRepoRootFile" AfterTargets="Build">
+    <WriteLinesToFile
+      File="$(OutputPath)tests_location.txt"
+      Lines="$(RepositoryRoot)/tests"
+      Overwrite="true"
+    />
+  </Target>
+
 </Project>
diff --git a/src/python_tests_runner/PythonTestRunner.cs b/src/python_tests_runner/PythonTestRunner.cs
@@ -8,22 +8,29 @@
 using NUnit.Framework;
 
 using Python.Runtime;
-using Python.Test;
 
 namespace Python.PythonTestsRunner
 {
     public class PythonTestRunner
     {
+        string OriginalDirectory;
+
         [OneTimeSetUp]
         public void SetUp()
         {
             PythonEngine.Initialize();
+            OriginalDirectory = Environment.CurrentDirectory;
+
+            var codeDir = File.ReadAllText("tests_location.txt").Trim();
+            TestContext.Progress.WriteLine($"Changing working directory to {codeDir}");
+            Environment.CurrentDirectory = codeDir;
         }
 
         [OneTimeTearDown]
         public void Dispose()
         {
             PythonEngine.Shutdown();
+            Environment.CurrentDirectory = OriginalDirectory;
         }
 
         /// <summary>
@@ -46,39 +53,15 @@ static IEnumerable<string[]> PythonTestCases()
         [TestCaseSource(nameof(PythonTestCases))]
         public void RunPythonTest(string testFile, string testName)
         {
-            // Find the tests directory
-            string folder = typeof(PythonTestRunner).Assembly.Location;
-            while (Path.GetFileName(folder) != "src")
+            using dynamic pytest = Py.Import("pytest");
+
+            using var args = new PyList();
+            args.Append(new PyString($"{testFile}.py::{testName}"));
+            int res = pytest.main(args);
+            if (res != 0)
             {
-                folder = Path.GetDirectoryName(folder);
+                Assert.Fail($"Python test {testFile}.{testName} failed");
             }
-            folder = Path.Combine(folder, "..", "tests");
-            string path = Path.Combine(folder, testFile + ".py");
-            if (!File.Exists(path)) throw new FileNotFoundException("Cannot find test file", path);
-
-            // We could use 'import' below, but importlib gives more helpful error messages than 'import'
-            // https://docs.python.org/3/library/importlib.html#importing-a-source-file-directly
-            // Because the Python tests sometimes have relative imports, the module name must be inside the tests package
-            PythonEngine.Exec($@"
-import sys
-import os
-sys.path.append(os.path.dirname(r'{folder}'))
-sys.path.append(os.path.join(r'{folder}', 'fixtures'))
-import clr
-clr.AddReference('Python.Test')
-import tests
-module_name = 'tests.{testFile}'
-file_path = r'{path}'
-import importlib.util
-spec = importlib.util.spec_from_file_location(module_name, file_path)
-module = importlib.util.module_from_spec(spec)
-sys.modules[module_name] = module
-try:
-  spec.loader.exec_module(module)
-except ImportError as error:
-  raise ImportError(str(error) + ' when sys.path=' + os.pathsep.join(sys.path))
-module.{testName}()
-");
         }
     }
 }
diff --git a/src/runtime/Util/PythonEnvironment.cs b/src/runtime/Util/PythonEnvironment.cs
@@ -161,7 +161,7 @@ private static Dictionary<string, string> TryParse(string venvCfg)
 
     private static string ProgramNameFromPath(string path)
     {
-        if (Runtime.IsWindows)
+        if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
         {
             return Path.Combine(path, "Scripts", "python.exe");
         }