Professional Visual Studio® 2008

20.2. Asserting the Facts

So far, this chapter has examined the structure of the test environment and how test cases are nested within test classes in a test project. What remains is to look at the body of the test case and review how test cases either pass or fail. (When a test case is generated, you saw that an Assert.Inconclusive statement is added to the end of the test to indicate that it is incomplete.)

The idea behind unit testing is that you start with the system, component, or object in a known state, and then run a method, modify a property, or trigger an event. The testing phase comes at the end, when you need to validate that the system, component, or object is in the correct state. Alternatively, you may need to validate that the correct output was returned from a method or property. You do this by attempting to assert a particular condition. If this condition is not true, the testing system reports this result and ends the test case. A condition is asserted, not surprisingly, via the Assert class. There is also a StringAssert class and a CollectionAssert class, which provide additional assertions for dealing with String objects and collections of objects, respectively.

20.2.1. Assert

The Assert class in the UnitTesting namespace, not to be confused with the Debug.Assert or Trace.Assert method in the System.Diagnostics namespace, is the primary class used to make assertions about a test case. The basic assertion has the following format:

Assert.IsTrue(variableToTest, ...