Update mstest0012.md (#42006)

Author: engyebrahim

docs/core/testing/mstest-analyzers/mstest0012.md

@@ -40,8 +40,12 @@ Methods marked with `[AssemblyInitialize]` should follow the following layout to
 - it should take one parameter of type `TestContext`
 - return type should be `void`, `Task` or `ValueTask`
 
-[!INCLUDE [test-class-rules](includes/test-class-rules.md)]
+The type declaring these methods should also respect the following rules:
 
+- The type should be a class.
+- The class should be public or internal (if the test project is using the [DiscoverInternals] attribute).
+- The class shouldn't be static.
+- The class should be marked with [TestClass] (or a derived attribute)
 - the class should not be generic
 
 ## How to fix violations