MSTEST0051: Assert.Throws should contain only a single statement

Cause

A call to Throws, ThrowsAsync, ThrowsExactly, or ThrowsExactlyAsync contains multiple statements in the action delegate.

Rule description

To ensure that only the specific method call that is expected to throw an exception is tested, the action delegate passed to Assert.Throws, Assert.ThrowsAsync, Assert.ThrowsExactly, or Assert.ThrowsExactlyAsync should contain exactly one statement. Including multiple statements can lead to passing tests when the exception is thrown by a statement that is not intended to throw. If it's not the last statement in the action that is intended to throw, then the test has dead code. If it's the last statement, the intent should be clearly stated.

How to fix violations

Refactor the test to ensure that the action delegate contains only the single statement that is expected to throw the exception. Move any setup code outside the assertion call.

For example, change this:

[TestMethod]
public void TestMethod()
{
    var obj = new MyClass();
    Assert.ThrowsExactly<InvalidOperationException>(() =>
    {
        obj.Initialize();
        obj.Execute(); // Only this should be inside the assertion
    });
}

To this:

[TestMethod]
public void TestMethod()
{
    var obj = new MyClass();
    obj.Initialize();
    Assert.ThrowsExactly<InvalidOperationException>(() => obj.Execute());
}

When to suppress warnings

Don't suppress warnings from this rule. Including multiple statements in the action delegate can make it unclear which operation is being tested and can lead to passing tests when the original intent is violated.