How do I use Assert to verify that an exception has been thrown?

Question

How do I use Assert (or other Test class) to verify that an exception has been thrown?

Answer 1

For "Visual Studio Team Test" it appears you apply the ExpectedException attribute to the test's method.

Sample from the documentation here: A Unit Testing Walkthrough with Visual Studio Team Test

[TestMethod] [ExpectedException(typeof(ArgumentException),     "A userId of null was inappropriately allowed.")] public void NullUserIdInConstructor() {    LogonInfo logonInfo = new LogonInfo(null, "P@ss0word"); } 

Answer 2

Usually your testing framework will have an answer for this. But if it's not flexible enough, you can always do this:

try {     somethingThatShouldThrowAnException();     Assert.Fail(); // If it gets to this line, no exception was thrown } catch (GoodException) { } 

As @Jonas points out, this DOES NOT work for catching a base Exception:

try {     somethingThatShouldThrowAnException();     Assert.Fail(); // raises AssertionException } catch (Exception) {     // Catches the assertion exception, and the test passes } 

If you absolutely must catch Exception, you need to rethrow the Assert.Fail(). But really, this is a sign you shouldn't be hand-writing this; check your test framework for options, or see if you can throw a more meaningful exception to test for.

catch (AssertionException) { throw; } 

You should be able to adapt this approach to whatever you like -- including specifying what kinds of exceptions to catch. If you only expect certain types, finish the catch blocks off with:

} catch (GoodException) { } catch (Exception) {     // not the right kind of exception     Assert.Fail(); }