In unittest, what argument should each test function include?

In the context of the unittest framework in Python, each test function should include the argument 'self' because each test case is typically defined within a class that inherits from unittest.TestCase. The 'self' parameter allows the test methods to have access to the instance of the test case class, enabling the use of instance attributes and methods.

When you define a test function as part of a TestCase class, 'self' serves as a reference point to access other methods and the testing framework's features provided by the unittest module, such as assertions. This is essential for organizing tests, sharing data between tests, and maintaining state throughout the lifetime of the test case instance.

Including 'self' also adheres to the conventions of Python class methods, making the test cases both clear and consistent with standard OOP practices in Python.