MSTEST0006: Avoid [ExpectedException]

Property	Value
Rule ID	MSTEST0006
Title	Avoid [ExpectedException]
Category	Design
Fix is breaking or non-breaking	Non-breaking
Enabled by default	Yes
Default severity	Info
Introduced in version	3.2.0

Cause

A method is marked with the [ExpectedException] attribute.

Rule description

Prefer Assert.ThrowsException or Assert.ThrowsExceptionAsync over the [ExpectedException] attribute as it ensures that only the expected line of code throws the expected exception, instead of acting on the whole body of the test. The assert APIs also provide more flexibility and allow you to assert extra properties of the exception.

[TestClass]
public class TestClass
{
    [TestMethod]
    [ExpectedException(typeof(InvalidOperationException))] // Violation
    public void TestMethod()
    {
        // Arrange
        var person = new Person
        {
            FirstName = "John", 
            LastName = "Doe",
        };
        person.SetAge(-1);

        // Act
        person.GrowOlder();
    }
}

How to fix violations

Replace the usage of the [ExpectedException] attribute by a call to Assert.ThrowsException or Assert.ThrowsExceptionAsync.

[TestClass]
public class TestClass
{
    [TestMethod]
    public void TestMethod()
    {
        // Arrange
        var person = new Person
        {
            FirstName = "John", 
            LastName = "Doe",
        };
        person.SetAge(-1);

        // Act
        Assert.ThrowsException(() => person.GrowOlder());
    }
}

When to suppress warnings

It is safe to suppress this diagnostic when the method is a one-liner.

[TestClass]
public class TestClass
{
    [TestMethod]
    [ExpectedException(typeof(ArgumentNullException))]
    public void TestMethod()
    {
        new Person(null);
    }
}