How can a unit test confirm an exception has been thrown

Question

Im writing a unit test for a c# class, One of my tests should cause the method to throw an exception when the data is added. How can i use my unit test to confirm that the exception has been thrown?

Answer 1

It depends on what unit test framework you're using. In all cases you could do something like:

[Test]
public void MakeItGoBang()
{
     Foo foo = new Foo();
     try
     {
         foo.Bang();
         Assert.Fail("Expected exception");
     }
     catch (BangException)
     { 
         // Expected
     }
}

In some frameworks there's an attribute you can add to the test method to express the expected exception, or there may be a method, such as:

[Test]
public void MakeItGoBang()
{
     Foo foo = new Foo();
     Assert.Throws<BangException>(() => foo.Bang());
}

It's nicer to limit the scope like this, as if you apply it to the whole test, the test could pass even if the wrong line threw the exception.

Answer 2

[ExpectedException(typeof(System.Exception))]

for Visual Studio Unit Testing Framework.

See MSDN:

The test method will pass if the expected exception is thrown.

The test will fail if the thrown exception inherits from the expected exception.