MSTEST0038: Don't use 'Assert.AreSame' or 'Assert.AreNotSame' with value types

Property	Value
Rule ID	MSTEST0038
Title	Don't use 'Assert.AreSame' or 'Assert.AreNotSame' with value types
Category	Usage
Fix is breaking or non-breaking	Non-breaking
Enabled by default	Yes
Default severity	Warning
Introduced in version	3.8.0
Is there a code fix	Yes

Cause

The use of Assert.AreSame or Assert.AreNotSame with one or both arguments being a value type.

Rule description

Assert.AreSame and Assert.AreNotSame work by comparing the reference of the given expected/notExpected and actual arguments via ReferenceEquals. Hence, when you pass a value type, it is boxed.

If using AreSame, the assert will always fail. If using AreNotSame, the assert will always pass.

For AreSame, the only case when the assert passes is if both arguments are nullable value types whose values are both null. In this case, it's clearer to have two separate Assert.IsNull calls.

How to fix violations

Use Assert.AreEqual and Assert.AreNotEqual instead of Assert.AreSame and Assert.AreNotSame. If using Assert.AreSame and both arguments are nullable value types whose values are expected to be null, then two separate Assert.IsNull calls might be a better fit than AreEqual, depending on the intent of the test.

When to suppress warnings

Do not suppress a warning from this rule. Ignoring this rule will result in an assertion that will always fail or always pass.