Follow @RoyOsherove on Twitter

Mocks and Stubs - The difference is in the flow of information

In class today when explaining the difference between stubs and mocks, I realized a simple explanation to this:

Stubs and mocks may seem the same but the flow of information from each is very different.

  • Stubs provide input for the application under test so that the test can be performed on something else.
  • Mocks provide input to the test to decide on pass\fail. the opposite direction.

The following diagram shows the flow of critical information:


The red arrows signify the "critical" flow of information that is used to decide if the test had passed. A stub can never fail a test, so there is no flow of information back to the test. the mock records things and then tells our test if it's expectations have been met according to its recording.

A stub is application facing, and a mock is test facing. Here's a more in depth overview of the two, but I haven't seen this explained as I just did anywhere. It's important to know and distinguish the two since many frameworks for mocking use these terms for different kinds of objects.

Synchronize Team System and ClearCase with the TFS Migration & Synchronization Tool

Tip: Easily change logon settings for all users on your machine