Testing

Running Tests with Nose

We created a suite of tests for our mean function, but it was annoying to run them one at a time. It would be a lot better if there were some way to run them all at once, just reporting which tests fail and which succeed.

Thankfully, that exists. Recall our tests:

from mean import *

def test_ints():
    num_list = [1,2,3,4,5]
    obs = mean(num_list)
    exp = 3
    assert obs == exp

def test_zero():
    num_list=[0,2,4,6]
    obs = mean(num_list)
    exp = 3
    assert obs == exp

def test_double():
    # This one will fail in Python 2
    num_list=[1,2,3,4]
    obs = mean(num_list)
    exp = 2.5
    assert obs == exp

def test_long():
    big = 100000000
    obs = mean(range(1,big))
    exp = big/2.0
    assert obs == exp

def test_complex():
    # given that complex numbers are an unordered field
    # the arithmetic mean of complex numbers is meaningless
    num_list = [2 + 3j, 3 + 4j, -32 - 2j]
    obs = mean(num_list)
    exp = NotImplemented
    assert obs == exp

Once these tests are written in a file called test_mean.py, the command “nosetests” can be called from the directory containing the tests:

$ nosetests

....F
======================================================================
FAIL: test_mean.test_complex
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/khuff/anaconda/envs/py3k/lib/python3.3/site-packages/nose/case.py", line 198, in runTest
    self.test(*self.arg)
  File "/Users/khuff/repos/2015-06-04-berkeley/testing/test_mean.py", line 34, in test_complex
    assert obs == exp
AssertionError

----------------------------------------------------------------------
Ran 5 tests in 3.746s

FAILED (failures=1)

In the above case, the python nose package ‘sniffed-out’ the tests in the directory and ran them together to produce a report of the sum of the files and functions matching the regular expression [Tt]est[-_]*.

The major boon a testing framework provides is exactly that, a utility to find and run the tests automatically. With nose, this is the command-line tool called nosetests. When nosetests is run, it will search all the directories whose names start or end with the word test, find all of the Python modules in these directories whose names start or end with test, import them, and run all of the functions and classes whose names start or end with test. In fact, nose looks for any names that match the regular expression '(?:^|[\\b_\\.-])[Tt]est'. This automatic registration of test code saves tons of human time and allows us to focus on what is important: writing more tests.

When you run nosetests, it will print a dot (.) on the screen for every test that passes, an F for every test that fails, and an E for every test were there was an unexpected error. In rarer situations you may also see an S indicating a skipped tests (because the test is not applicable on your system) or a K for a known failure (because the developers could not fix it promptly). After the dots, nosetests will print summary information.

$ nosetests

.....

Ran 5 tests in 3.746s

OK

As we write more code, we would write more tests, and nosetests would produce more dots. Each passing test is a small, satisfying reward for having written quality scientific software. Now that you know how to write tests, let’s go into what can go wrong.