Edit

MSTEST0075: Avoid changing the current directory in a parallelized test

Property Value
Rule ID MSTEST0075
Title Avoid changing the current directory in a parallelized test
Category Usage
Fix is breaking or non-breaking Non-breaking
Enabled by default Yes
Default severity Info
Introduced in version 4.4.0 (preview)
Is there a code fix Yes, for C# only

Important

ResourceLockAttribute is planned for MSTest 4.4 and is available only in preview builds until MSTest 4.4.0 is released.

Note

This analyzer activates only when assembly parallelization is syntactically enabled, for example through [assembly: Parallelize] without a matching [assembly: DoNotParallelize], or when a .editorconfig file sets mstest_parallel_safety_mode = always. The analyzer can't detect parallelization that's enabled only through .runsettings or MSBuild properties such as MSTestParallelizeWorkers. Set the .editorconfig option if you configure parallelization that way and still want this analyzer to run.

Cause

A test, or a class-scoped fixture method it runs under, calls Directory.SetCurrentDirectory or assigns Environment.CurrentDirectory without a matching [ResourceLock] or [DoNotParallelize].

Rule description

The current directory is process-global on every operating system and, unlike culture, has no thread-scoped or async-scoped equivalent. A test that changes it corrupts the working directory of every test running concurrently, and relative paths resolved elsewhere in the suite silently point at the wrong location.

[TestMethod]
public void ChangesDirectory()
{
    Directory.SetCurrentDirectory(tempPath); // Violation
}

How to fix violations

Declare [ResourceLock(WellKnownResources.CurrentDirectory)] to serialize contending tests, or add [DoNotParallelize] to opt the test out of parallelization. Even with a lock, prefer passing absolute paths so the current directory never needs to change.

[ResourceLock(WellKnownResources.CurrentDirectory)]
[TestMethod]
public void ChangesDirectory()
{
    Directory.SetCurrentDirectory(tempPath);
}

A C# code fix adds the [ResourceLock] attribute for you, at the test method or, for a class-scoped fixture such as [TestInitialize], at the test class. Visual Basic code has this diagnostic but doesn't have an automatic fix; add the attribute by hand.

When to suppress warnings

Don't suppress warnings from this rule without declaring a lock or opting out of parallelization, because doing so leaves the mutation racing silently against concurrently running tests.

Suppress a warning

If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

#pragma warning disable MSTEST0075
// The code that's violating the rule is on this line.
#pragma warning restore MSTEST0075

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

[*.{cs,vb}]
dotnet_diagnostic.MSTEST0075.severity = none

For more information, see How to suppress code analysis warnings.

See also

  • Last updated on