MSTEST0067: Avoid synchronously blocking calls in test code

Property	Value
Rule ID	MSTEST0067
Title	Avoid synchronously blocking calls in test code
Category	Usage
Fix is breaking or non-breaking	Non-breaking
Enabled by default	No
Default severity	Info
Introduced in version	4.3.0
Is there a code fix	No

Note

This rule is available starting with MSTest 4.3. It's disabled by default. It's enabled as a warning when <MSTestAnalysisMode>All</MSTestAnalysisMode> is set.

Cause

Test code uses a synchronously blocking call such as Thread.Sleep, Task.Wait, Task.WaitAll, Task.WaitAny, or Task<TResult>.Result.

The rule fires on methods marked with TestMethodAttribute (including custom attributes that inherit from it) and on fixture methods marked with TestInitializeAttribute, TestCleanupAttribute, ClassInitializeAttribute, ClassCleanupAttribute, AssemblyInitializeAttribute, AssemblyCleanupAttribute, GlobalTestInitializeAttribute, and GlobalTestCleanupAttribute.

Rule description

Synchronously blocking the current thread inside test methods or test fixtures is a common source of flakiness and can also deadlock when the test framework runs tests on a synchronization context that requires cooperative scheduling. Prefer await Task.Delay for time-based waits and await the task to observe its result.

[TestClass]
public class TestClass
{
    [TestMethod]
    public async Task Test()
    {
        Thread.Sleep(1000); // Violation
        var result = ComputeAsync().Result; // Violation
        ComputeAsync().Wait(); // Violation
    }

    private static Task<int> ComputeAsync() => Task.FromResult(42);
}

How to fix violations

Use the asynchronous equivalent:

[TestClass]
public class TestClass
{
    [TestMethod]
    public async Task Test()
    {
        await Task.Delay(1000);
        var result = await ComputeAsync();
    }

    private static Task<int> ComputeAsync() => Task.FromResult(42);
}

When to suppress warnings

This rule is disabled by default. When opted-in, suppress individual occurrences when the synchronous wait is intentional and not avoidable — for example, when interacting with a synchronous API that cannot be made asynchronous.

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 MSTEST0067
// The code that's violating the rule is on this line.
#pragma warning restore MSTEST0067

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

[*.{cs,vb}]
dotnet_diagnostic.MSTEST0067.severity = none

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