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MSTEST0074: Test mutating process-global state should declare a resource lock

Property Value
Rule ID MSTEST0074
Title Test mutating process-global state should declare a resource lock
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 Environment.SetEnvironmentVariable or Console.SetOut/SetError/SetIn without a matching [ResourceLock] or [DoNotParallelize].

Rule description

Mutating process-global state, such as environment variables or console redirection, from a test is unsafe once in-assembly parallelization is enabled, because a sibling test running concurrently observes the mutation. Unlike [ResourceLock], which fails open when a key is forgotten, this rule flags the mutation at compile time.

[TestMethod]
public void SetsVariable()
{
    Environment.SetEnvironmentVariable("MODE", "test"); // Violation
}

How to fix violations

Declare [ResourceLock] with the matching WellKnownResources key to serialize contending tests, or add [DoNotParallelize] to opt the test out of parallelization.

[ResourceLock(WellKnownResources.EnvironmentVariables)]
[TestMethod]
public void SetsVariable()
{
    Environment.SetEnvironmentVariable("MODE", "test");
}

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 MSTEST0074
// The code that's violating the rule is on this line.
#pragma warning restore MSTEST0074

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

[*.{cs,vb}]
dotnet_diagnostic.MSTEST0074.severity = none

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

See also

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