Sometimes we have tests that should only run in a particular context. For example, we might have a group of tests that only runs on the Windows operating system but not Linux or macOS. For these situations, it’s helpful to be able to skip tests.

The unittest framework provides two different ways to skip tests:

1. The @unittest skip decorator
2. The skipTest() method

First, let’s examine the skip decorator option. There are two decorator options to accomplish the goal of skipping a test. Let’s observe both of them in the example below:

import sys

class LinuxTests(unittest.TestCase):

    @unittest.skipUnless(sys.platform.startswith("linux"), "This test only runs on Linux")
    def test_linux_feature(self):
        print("This test should only run on Linux")

    @unittest.skipIf(not sys.platform.startswith("linux"), "This test only runs on Linux")
    def test_other_linux_feature(self):
        print("This test should only run on Linux")

Let’s break down both skip decorator options:

• The skipUnless option skips the test if the condition evaluates to False.

• The skipIf option skips the test if the condition evaluates to True.

Both share common requirements. Firstly, both of these skip decorators are prefaced with @unittest to denote the decorator pattern. They both take a condition as a first argument, followed by a string message as the second. In this example, both decorators achieve the same goal: skipping the test if the operating system is not Linux.

If we ran the tests on a macOS system, we would get the following output:

ss
----------------------------------------------------------------------
Ran 2 tests in 0.000s

OK (skipped=2)

The second way to skip tests is to call the skipTest method of the TestCase class, as in this example:

import sys

class LinuxTests(unittest.TestCase):

    def test_linux_feature(self):
        if not sys.platform.startswith("linux"):
            self.skipTest("Test only runs on Linux")

Here we call self.skipTest() from within the test function itself. It takes a single string message as its argument and always causes the test to be skipped when called. When run on macOS we get the following output:

s
----------------------------------------------------------------------
Ran 1 test in 0.000s

OK (skipped=1)

Skip decorators are slightly more convenient and make it easy to see under what conditions the test is skipped. When the conditions for skipping a test are too complicated to pass into a skip decorator, the skipTest method is the recommended alternative.

Let’s practice skipping tests in our Small World Air application!