In order to make a test for the code inside myfile.py we create a file test_myfile.py. Inside test_myfile.py we will write the different tests for the methods found in myfile.py.

In order to create a test for a function my_function we create a class TestMyFunction(unittest.TestCase) which will contain inside different functions that will test different aspects about my_function.

For example, the following test class named TestCircleArea should test circle_area. Inside the class we have two types of tests.

• def test_area(self) tests if the results of the function are correct. That is, for different inputs, we should know the output and check if they match.

• def test_values(self) tests if the values provided as input raise the appropiate error when they are outside the domain of the function.

class TestCircleArea(unittest.TestCase):
    def test_area(self):
        # test areas
        self.assertAlmostEqual(circle_area(1), pi)
        self.assertAlmostEqual(circle_area(2.1), pi*2.1**2)
        self.assertAlmostEqual(circle_area(0), 0)
         
    def test_values(self):
        # Make sure errors are raised when necessary
        self.assertRaises(ValueError, circle_area, -2)

In order to run the tests, run in the terminal

python -m unittest test_circles.py

This should print the results of the tests

There is an alternative/additional way to make tests. Python tests can be done in the documentation of functions (inside the sting). To do this you need to add

>>> myfunction(value)
output

For example, for a function that doubles a number we would have:

>>> double(5)
10

In order to run all the doctests from a file my_file.py you would run

python my_file.py -v

You need inside the file my_file.py the following code:

if __name__ == "__main__":
    import doctest
    doctest.testmod()

This code tells python to check the doctest (allways not in the event of -v). Moreover, if called with -v it will print the results of the tests. This means that if a tests fails it is displayed even if you do not run the scirpt with -v, but if all tests are passed nothing will be printed unless you call the file explicitly with -v.

There is an alternative way to check doctests without having a main in a file. You can run

python -m doctest my_file.py  -v

to asses if all the doctests are passed.

You can try for example

python -m doctest factorial_withoutmain.py  -v

Try running python factorial_wrong.py without the -v and the code will produce:

python factorial_wrong.py 
**********************************************************************
File "factorial_wrong.py", line 6, in __main__
Failed example:
    factorial(5)
Expected:
    120
Got:
    0
**********************************************************************
File "factorial_wrong.py", line 13, in __main__.factorial
Failed example:
    [factorial(n) for n in range(6)]
Expected:
    [1, 1, 2, 6, 24, 120]
Got:
    [0, 0, 0, 0, 0, 0]
**********************************************************************
File "factorial_wrong.py", line 15, in __main__.factorial
Failed example:
    factorial(30)
Expected:
    265252859812191058636308480000000
Got:
    0
**********************************************************************
File "factorial_wrong.py", line 27, in __main__.factorial
Failed example:
    factorial(30.0)
Expected:
    265252859812191058636308480000000
Got:
    0
**********************************************************************
2 items had failures:
   1 of   1 in __main__
   3 of   6 in __main__.factorial
***Test Failed*** 4 failures.

Nevertheless python factorial.py will not produce anything because the tests in the docstrings do not crush.

Notice that this behaviour happens because factorial_wrong.py has the main:

if __name__ == "__main__":
    import doctest
    doctest.testmod()

If you remove the main this will not happen (no errors will be printed).

The code in factorial.py contains some doctests.

If you run

python factorial.py -v

You should see a bunch of outputs with the different tests.

Notice that factorial_withoutmain.py does not have a doctest.testmod() call. Therefore

python factorial_withoutmain.py  -v

will not print anything.