Test Doubles

Test Doubles

Gerard Meszaros introduces the concept of Test Doubles in [Meszaros2007] like this:

Sometimes it is just plain hard to test the system under test (SUT) because it depends on other components that cannot be used in the test environment. This could be because they aren't available, they will not return the results needed for the test or because executing them would have undesirable side effects. In other cases, our test strategy requires us to have more control or visibility of the internal behavior of the SUT.

When we are writing a test in which