MSTEST0004: Public types should be test classes

Cause

A public type is not a test class (class marked with the [TestClass] attribute).

Rule description

To distinguish runnable tests from support code, reserve publicly visible concrete classes for test classes and keep helper classes internal when possible. This opt-in design rule helps you notice a missing [TestClass] attribute or an unintentionally public helper.

Public helper classes aren't invalid MSTest code. The rule enforces a project convention, not a discovery requirement, and doesn't report abstract or static classes.

How to fix violations

Change the accessibility of the type to not be public.

When to suppress warnings

Suppress the diagnostic when a helper must remain public for another assembly or an existing contract. A deliberately public helper doesn't become a test class unless it has [TestClass] or a derived attribute.

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 MSTEST0004
// The code that's violating the rule is on this line.
#pragma warning restore MSTEST0004

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

[*.{cs,vb}]
dotnet_diagnostic.MSTEST0004.severity = none

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