Example Unit Test
^^^^^^^^^^^^^^^^^^
Unit tests are small functions that test other functions by calling them,
usually with a set of ``dummy`` inputs, or inputs that you know will yield a
consistent result. The purpose is to make sure the function does more or less
what it is supposed to do.

This can be done by inputting either reasonable values to check that the function returns something sensible, or something unreasonable to check that it returns something less sensible or breaks as it’s supposed to. They can also test the shape and type of outputs given some input. 

From the above example function a simple unit test could be:

.. code-block:: python

    def my_function(a, b=1):
        """ Add two numbers

        This should be a descriptive docstring, but we will
        skip it for now. 
        
        """

        c = a+b

        return c


    def test_my_function():
        """ Test my_function
        
        Test functions can have docstrings too.
        
        """
    
        import pytest
        import numpy as np

        # These are sensibile input/output checks
        assert(my_function(1)==2)
        assert(my_function(1,2)==3)

        # This is a break test
        with pytest.raises(TypeError):
            assert(my_function(1, 'adding a string to an integer should raise a TypeError'))

        # This is a shape test
        d = array([1,2])
        result =  my_function(d, 1)
        assert(np.shape(result) == np.shape(d))   

A single test function can contain multiple smaller tests.