Time for action – writing a unit test

We will write tests for a simple factorial function. The tests will check for the so called happy path and for abnormal conditions.

1. We start by writing the factorial function

   def factorial(n):
     if n == 0:
       return 1
   
     if n < 0:
       raise ValueError, "Unexpected negative value"
   
     return np.arange(1, n+1).cumprod()

   The code is using the arange and cumprod functions we have already seen to create arrays and calculate the cumulative product, but we added a few checks for boundary conditions.

2. Now we will write the unit test. Let's write a class that will contain the unit tests. It extends the TestCase class from the unittest module which is part of standard Python. We test for calling the factorial function with:

   • a positive number, the happy path

   • boundary condition 0

   • negative numbers, which should result in an error

     class FactorialTest(unittest.TestCase):
       def test_factorial(self):
         #Test for the factorial of 3 that should pass.
         self.assertEqual(6...