Assert.IsNotAssignableFrom
Assert.IsNotAssignableFrom succeeds if the object provided may not be assigned a value of the expected type.
Note
From version 4.5.0, using C# 14, you don't need to use the ClassicAssert class, nor the NUnit.Framework.Legacy namespace, but can use the former Assert class. This applies for many of the asserts, but a few still require the use of the ClassicAssert class. These will be fixed in upcoming releases. In the list below, and in the examples, the 4.5.0 syntax will be used. If you use an earlier 4.x version, replace Assert with ClassicAssert and include the NUnit.Framework.Legacy namespace.
Assert.IsNotAssignableFrom(Type expected, object actual);
Assert.IsNotAssignableFrom(Type expected, object actual,
string message, params object[] params);
Assert.IsNotAssignableFrom<T>(object actual);
Assert.IsNotAssignableFrom<T>(object actual,
string message, params object[] params);