Why is this an issue?

It should be clear to a casual reader what code a test is testing and what results are expected. Unfortunately, that’s not usually the case with the ExpectedException attribute since an exception could be thrown from almost any line in the method.

This rule detects MSTest and NUnit ExpectedException attribute.

Exceptions

This rule ignores:

[TestMethod]
[ExpectedException(typeof(InvalidOperationException))]
public void UsingTest()
{
    Console.ForegroundColor = ConsoleColor.Black;
    try
    {
        using var _ = new ConsoleAlert();
        Assert.AreEqual(ConsoleColor.Red, Console.ForegroundColor);
        throw new InvalidOperationException();
    }
    finally
    {
        Assert.AreEqual(ConsoleColor.Black, Console.ForegroundColor); // The exception itself is not relevant for the test.
    }
}

public sealed class ConsoleAlert : IDisposable
{
    private readonly ConsoleColor previous;

    public  ConsoleAlert()
    {
        previous = Console.ForegroundColor;
        Console.ForegroundColor = ConsoleColor.Red;
    }

    public void Dispose() =>
        Console.ForegroundColor = previous;
}

How to fix it in MSTest

Remove the ExpectedException attribute in favor of using the Assert.ThrowsException assertion.

Code examples

Noncompliant code example

[TestMethod]
[ExpectedException(typeof(ArgumentNullException))]  // Noncompliant
public void Method_NullParam()
{
    var sut = new MyService();
    sut.Method(null);
}

Compliant solution

[TestMethod]
public void Method_NullParam()
{
    var sut = new MyService();
    Assert.ThrowsException<ArgumentNullException>(() => sut.Method(null));
}

How to fix it in NUnit

Remove the ExpectedException attribute in favor of using the Assert.Throws assertion.

Code examples

Noncompliant code example

[Test]
[ExpectedException(typeof(ArgumentNullException))]  // Noncompliant
public void Method_NullParam()
{
    var sut = new MyService();
    sut.Method(null);
}

Compliant solution

[Test]
public void Method_NullParam()
{
    var sut = new MyService();
    Assert.Throws<ArgumentNullException>(() => sut.Method(null));
}

Resources

Documentation