Looking through your code line by line to spot errors.

Testing the program without access to the source code.

Testing together a number of different features that have been developed independently

Testing every possible outcome for a function by viewing the code and testing each branch.

Creating a number of empty functions that return default values so that you can test other features during the development phase.

Asking a small number of users from outside the development team (but usually inside the organisation) to test the program and give feedback.

Asking a large number of users from outside the organisation to test the program prior to release and give feedback to the developers

The final check performed with client and users to ensure that the system is functionally fully as expected.

Adding a new feature to a program that wasn't required earlier.

Rolling out a patch for a critical security bug