A4 portrait - PET: Python Entre Todos - Python Argentina

How should the test be? 18
test_find_roots
Given a list of coefficients and its roots, test that the result of the roots obtained
from that coefficient matches the expected result. This test checks that
find_roots works correctly. To do that, we iterate over a list of two tuples:
• A tuple with the coefficients to call the function.
• A tuple with the roots expected for those coefficients. These roots were
calculated manually, not using the program.
test_form_polynomial
Given a list of roots, check that the coefficients are correct. This test checks that
form_polynomial works correctly. In this case it’s a list of two tuples:
• One with the roots
• Th second with the coefficients expected for those roots.
test_cant_find_roots
Check that find_roots raises the right exception when real roots can’t be found.
test_not_quadratic
Checks what happens when the coefficients don’t belong to a quadratic
function.
test_integrity
Given a set of roots, finds the coefficients, and for those coefficients find the
roots again. The result of the roundtrip should be the same we started with.
test_integrity_fails
Check the case where integrity fails. In this case we use functions whose a
value is not 1, so even if the roots are the same, it’s not the same quadratic
function.
4. At the end of the test we put this code:
if __name__ == '__main__':
unittest.main()
That way, if we run python filename.py it will enter that if, and run all the tests
in this file.
Suppose we are in the folder where these files reside:
pymag@localhost:/home/pymag$ ls
polynomial.py test_polynomial.py test_polynomial_fail.py
So, let’s run the passing tests:
pymag@localhost:/home/pymag$ python test_polynomial.py
......
----------------------------------------------------------------------
Ran 6 tests in 0.006s
OK
The output shows that all 6 tests in this class ran, and they all passed. Now we’ll see
what happens when a test fails. For this, what I did was change one of the tests so
that the second root is smaller than the first. I changed test_integrity so that one of
the expected roots is (2, 1), when it should really be (1, 2) since the first root should
be smaller. This is in test_polynomial_fail.py. So, if we run the tests that fail, we see:
pymag@localhost:/home/pymag$ python test_polynomial_fail.py
..F...
======================================================================
FAIL: test_integrity (test_polynomial.Testpolynomial)
----------------------------------------------------------------------
PET: English Translation (Issue 1, August 2010) — http://revista.python.org.ar