Twisted Network Programming Essentials, 2nd Edition

Chapter 11. Testing

Because Twisted programs are event-driven and use Deferreds to wait for and handle events, we can’t easily use standard testing frameworks like Python’s unittest to write tests for them.

To handle this, Twisted comes with an extension of Python’s unittest framework for testing event-driven Twisted programs, and a command-line utility for running them. These components comprise Trial, Twisted’s testing framework.

Writing and Running Twisted Unit Tests with Trial

Tests that don’t exercise event-driven logic import twisted.trial.unittest instead of unittest but otherwise look identical to traditional Python unittest tests.

Example 11-1 shows a single test case class called MyFirstTestCase, containing a single test called test_something, which makes an assertion using the Twisted version of unittest’s TestCase.assertTrue. Most unittest assertions have Twisted versions, and Trial has additional assertions for exercising Failures.

Example 11-1. test_foo.py

from twisted.trial import unittest

class MyFirstTestCase(unittest.TestCase):
    def test_something(self):
        self.assertTrue(True)

We can use the trial command-line utility that ships with Twisted to run the test file:

$ trial test_foo.py
test_foo
  MyFirstTestCase
    test_something ...                                                     [OK]

-------------------------------------------------------------------------------
Ran 1 tests in 0.002s

PASSED (successes=1)

We can run individual test classes by specifying the class name, as in:

trial test_foo.MyFirstTestCase

and run individual tests ...