To check for bugs and viruses.
To get the most out of an app.
To compare the results with other tests.
To see whether the given module works.
Calling the tested method
How many hidden bugs does the app contain
How many users did access the test
How many times function calls were called
How many people online can view your app
A fake password given to beta testers
A fake method with a pre-programmed behavior and expectations
A bad phrase said to insult someone
A fake method used to crack codes
They replace the target function
You can use stubs to control a method's behavior
You can use stubs to prevent calls to external resources
You must use it in every step