Python Unit Tests

This files covers unit testing in Python. Unit testing has several benefits:

It provides a means of testing your code to ensure it works as you expect it to work
It documents the features and behaviors of your class
It helps you confirm that any changes you make to your code did not break existing features

There are other important aspects to unit testing, but the three points outlined above provide a simple, easy to understand starting point for a technology that is really more than a technology, and that can be thought of as a philosophy for architecting and managing projects.

Simple Example

In this section you will see a simple example of how to write a few simple tests. First I will show you a program that does some simply File IO. Then I will show you code that tests these operations to confirm that they work as expected. In particular, the code tests to see if a method that is designed to write and read from a file actually creates a file, and actually writes and reads the expected value from the file. This example is not meant to be an exhaustive test of the sample class, but rather a demonstration of who to use the basic syntax of unit testing.

Watch the Video: http://youtu.be/fU7RHewj6dg

The file to test:

#!/usr/bin/python

class SimpleFile(object):

    def __init__(self, fileName):
        self.fileName = fileName

    def write_text(self, textToWrite):
        f = open(self.fileName, 'w')
        f.write(textToWrite)
        f.close()

    def read_text(self):
        f = open(self.fileName, 'r')
        read = f.read()
        return read

The file that tests it contains several important features:

import unittest
The main class begins with the word Test and inherits from unittest.TestCase
The actual test methods all begin with the word test

You must have these features in your unit tests. For instance, the way you tell the unit test library that a particular method is a test is to have it begin with the word test.

#!/usr/bin/python

import unittest
import os
from files.core import SimpleFile

class Test(unittest.TestCase):

    def get_file_name(self):
        fileName = "bar.txt"
        return fileName

    def get_file_text(self):
        textToWrite = "This line"
        return textToWrite

    def test_write_file(self):        
        simple_file = SimpleFile(self.get_file_name())
        simple_file.write_text(self.get_file_text())
        self.assertTrue(os.path.isfile(self.get_file_name()))

    def test_read_file(self):
        simple_file = SimpleFile(self.get_file_name())
        read_text = simple_file.read_text()
        self.assertEqual(read_text,self.get_file_text())

suite = unittest.TestLoader().loadTestsFromTestCase(Test)
unittest.TextTestRunner(verbosity=2).run(suite)

Set Up

If you have something that you want to do before each test is run, add a setup method to your testcase:

class Test(unittest.TestCase):
    def setUp(self):
        self.chords = SimpleDbChords("Chords")
        self.contentType = self.chords.getHeader()

Just as setUp() runs before each test, a method called tearDown() will be run after each test. It is important to understand that this is very different from a constructor or destructor. The setUp and testDown methods are not called when the object is created or destroyed, but rather before and after each test is run.\