##########################
Part 4: Running the script
##########################

Running *python test.py* will invoke the
SquarerTest.test_positive_numbers method and also the
SquarerTest.test_negative_numbers method. If our Squarer.calc method
is working as we expect it to, if it conforms to the behavior we defined
in the *squares* dictionary, then nothing will be printed to the
console. On the other hand, if the SquarerTest finds discrepancies in the behavior of
Squarer, then it will print those discrepancies to the console.

Since *squarer.py* has an error that the other developer just introduced, here is
the result of running *python test.py*:

::

    $ python test.py
    Squared 3 and got 27 but expected 9
    Squared 12 and got 8916100448256 but expected 144
    Squared 100 and got 100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 but expected 10000
    Squared -1 and got -1.0 but expected 1
    Squared -2 and got 0.25 but expected 4
    Squared -3 and got -0.037037037037037035 but expected 9
    Squared -12 and got 1.1215665478461509e-13 but expected 144
    Squared -100 and got 1e-200 but expected 10000

    $

Let's go back into squarer.py and fix our mistake:

.. raw:: html

   <div
   style#"background: #ffffff; overflow: auto; width: auto; border: solid gray; border-width: .1em .1em .1em .8em; padding: .2em .6em;">

::

    # squarer.py
    class Squarer(object):

        @staticmethod
        def calc(operand):
            # return operand*operand   # OLD
            # return operand**operand  # WRONG
            return operand*operand


Has this actually fixed our code? Let's run our test script to find out:

::

    $ python test.py

    $

Running test.py produces no errors: test.py was not able to find any
discrepancies between the expected behavior that we defined for
Squarer's calc method and the method's actual behavior. 

Suppose you wanted to revise squarer.py one more time. You want to try
another implementation of the calc method that uses the power operator:

.. raw:: html

   <div
   style#"background: #ffffff; overflow: auto; width: auto; border: solid gray; border-width: .1em .1em .1em .8em; padding: .2em .6em;">

::

    # squarer.py
    class Squarer(object):

        @staticmethod
        def calc(operand):
            # return operand*operand   # OLD
            # return operand**operand  # WRONG
            # return operand*operand   # OLD
            return operand**2


By putting our test into a script file that we can run from the command
line, we've made it so that it only takes a few seconds to test whether
we've introduced an error into our code. We run our test script:

::

    $ python test.py

    $

The test script has not found any discrepancies between the *expected*
and *actual* performance of Squarer.calc: it looks
like *operand**2* is an acceptable way to implement squaring!