MSTEST0059: Do not use both Parallelize and DoNotParallelize attributes

Cause

An assembly contains both ParallelizeAttribute and DoNotParallelizeAttribute attributes.

Rule description

The ParallelizeAttribute and DoNotParallelizeAttribute attributes are mutually exclusive at the assembly level. When both attributes are applied to the same assembly, tests run sequentially. This conflicting configuration indicates unclear intent and should be resolved by choosing one parallelization strategy for your test assembly.

using Microsoft.VisualStudio.TestTools.UnitTesting;

[assembly: Parallelize(Workers = 0, Scope = ExecutionScope.MethodLevel)] // Violation
[assembly: DoNotParallelize]

How to fix violations

Remove one of the conflicting attributes based on your intended parallelization strategy.

If you want parallel execution:

using Microsoft.VisualStudio.TestTools.UnitTesting;

[assembly: Parallelize(Workers = 0, Scope = ExecutionScope.MethodLevel)]

If you want sequential execution:

using Microsoft.VisualStudio.TestTools.UnitTesting;

[assembly: DoNotParallelize]

If you want to enable parallelization at the assembly level but disable it for specific classes or methods, apply Parallelize at the assembly level and DoNotParallelize at the class or method level:

using Microsoft.VisualStudio.TestTools.UnitTesting;

[assembly: Parallelize(Workers = 0, Scope = ExecutionScope.MethodLevel)]

[DoNotParallelize]
[TestClass]
public class SequentialTests
{
    [TestMethod]
    public void Test1() { }
}

[TestClass]
public class ParallelTests
{
    [TestMethod]
    public void Test2() { }
    
    [DoNotParallelize]
    [TestMethod]
    public void Test3() { }
}

When to suppress warnings

Do not suppress warnings from this rule. Having both attributes creates ambiguous test configuration that should be resolved.

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 MSTEST0059
// The code that's violating the rule is on this line.
#pragma warning restore MSTEST0059

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

[*.{cs,vb}]
dotnet_diagnostic.MSTEST0059.severity = none

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