guides-good_tests

This document is an introduction to writing good autopilot tests. This should be treated as additional material on top of all the things you’d normally do to write good code. Put another way: test code follows all the same rules as production code - it must follow the coding standards, and be of a professional quality.

Several points in this document are written with respect to the unity autopilot test suite. This is incidental, and doesn’t mean that these points do not apply to other test suites!

Write Expressive Tests

Unit tests are often used as a reference for how your public API should be used. Functional (Autopilot) tests are no different: they can be used to figure out how your application should work from a functional standpoint. However, this only works if your tests are written in a clear, concise, and most importantly expressive style. There are many things you can do to make your tests easier to read:

Pick Good Test Case Class Names

Pick a name that encapsulates all the tests in the class, but is as specific as possible. If necessary, break your tests into several classes, so your class names can be more specific. This is important because when a test fails, the test id is the primary means of identifying the failure. The more descriptive the test id is, the easier it is to find the fault and fix the test.

Pick Good Test Case Method Names

Similar to picking good test case class names, picking good method names makes your test id more descriptive. We recommend writing very long test method names, for example:

# bad example:
def test_save_dialog(self):
# test goes here
# better example:
def test_save_dialog_can_cancel(self):
# test goes here
# best example:
def test_save_dialog_cancels_on_escape_key(self):
# test goes here

Write Docstrings

You should write docstrings for your tests. Often the test method is enough to describe what the test does, but an English description is still useful when reading the test code. For example:

def test_save_dialog_cancels_on_escape_key(self):
"""The Save dialog box must cancel when the escape key is pressed."""

We recommend following href="http://www.python.org/dev/peps/pep-0257">PEP 257 when writing all docstrings.

Test One Thing Only

Tests should test one thing, and one thing only. Since we’re not writing unit tests, it’s fine to have more than one assert statement in a test, but the test should test one feature only. How do you tell if you’re testing more than one thing? There’s two primary ways:

  • Can you describe the test in a single sentence without using words like ‘and’, ‘also’, etc? If not, you should consider splitting your tests into multiple smaller tests.
  • Tests usually follow a simple pattern:
  • Set up the test environment.
  • Perform some action.
  • Test things with assert statements.

    • If you feel you’re repeating steps ‘b’ and ‘c’ you’re likely testing more than one thing, and should consider splitting your tests up.

    Good Example:

    def test_alt_f4_close_dash(self):
"""Dash must close on alt+F4."""
self.dash.ensure_visible()
self.keyboard.press_and_release("Alt+F4")
self.assertThat(self.dash.visible, Eventually(Equals(False)))

    This test tests one thing only. Its three lines match perfectly with the typical three stages of a test (see above), and it only tests for things that it’s supposed to. Remember that it’s fine to assume that other parts of unity work as expected, as long as they’re covered by an autopilot test somewhere else - that’s why we don’t need to verify that the dash really did open when we called self.dash.ensure_visible().

    Fail Well

    Make sure your tests test what they’re supposed to. It’s very easy to write a test that passes. It’s much more difficult to write a test that only passes when the feature it’s testing is working correctly, and fails otherwise. There are two main ways to achieve this:

    • Write the test first. This is easy to do if you’re trying to fix a bug in Unity. In fact, having a test that’s exploitable via an autopilot test will help you fix the bug as well. Once you think you have fixed the bug, make sure the autopilot test you wrote now passed. The general workflow will be:
  • Branch unity trunk.
  • Write autopilot test that reproduces the bug.
  • Commit.
  • Write code that fixes the bug.
  • Verify that the test now passes.
  • Commit. Push. Merge.
  • Celebrate!
    • If you’re writing tests for a bug-fix that’s already been written but is waiting on tests before it can be merged, the workflow is similar but slightly different:
  • Branch unity trunk.
  • Write autopilot test that reproduces the bug.
  • Commit.
  • Merge code that supposedly fixes the bug.
  • Verify that the test now passes.
  • Commit. Push. Superseed original merge proposal with your branch.
  • Celebrate!

    • Think about design

    Much in the same way you might choose a functional or objective-oriented paradigm for a piece of code, a testsuite can benefit from choosing a good design pattern. One such design pattern is the page object model. The page object model can reduce testcase complexity and allow the testcase to grow and easily adapt to changes within the underlying application. Check out Page Object Pattern.

    Test Length

    Tests should be short - as short as possible while maintaining readability. Longer tests are harder to read, harder to understand, and harder to debug. Long tests are often symptomatic of several possible problems:

  • Your test requires complicated setup that should be encapsulated in a method or function.
  • Your test is actually several tests all jammed into one large test.

    • Bad Example:

    def test_panel_title_switching_active_window(self):
"""Tests the title shown in the panel with a maximized application."""
# Locked Launchers on all monitors
self.set_unity_option('num_launchers', 0)
self.set_unity_option('launcher_hide_mode', 0)
text_win = self.open_new_application_window("Text Editor", maximized=True)
self.assertTrue(text_win.is_maximized)
self.assertThat(self.panel.title, Equals(text_win.title))
sleep(.25)
calc_win = self.open_new_application_window("Calculator")
self.assertThat(self.panel.title, Equals(calc_win.application.name))
icon = self.launcher.model.get_icon_by_desktop_id(text_win.application.desktop_file)
launcher = self.launcher.get_launcher_for_monitor(self.panel_monitor)
launcher.click_launcher_icon(icon)
self.assertTrue(text_win.is_focused)
self.assertThat(self.panel.title, Equals(text_win.title))

    This test can be simplified into the following:

    def test_panel_title_switching_active_window(self):
"""Tests the title shown in the panel with a maximized application."""
text_win = self.open_new_application_window("Text Editor", maximized=True)
self.open_new_application_window("Calculator")
icon = self.launcher.model.get_icon_by_desktop_id(text_win.application.desktop_file)
launcher = self.launcher.get_launcher_for_monitor(self.panel_monitor)
launcher.click_launcher_icon(icon)
self.assertTrue(text_win.is_focused)
self.assertThat(self.panel.title, Equals(text_win.title))

    Here’s what we changed:

  • Removed the set_unity_option lines, as they didn’t affect the test results at all.
  • Removed assertions that were duplicated from other tests. For example, there’s already an autopilot test that ensures that new applications have their title displayed on the panel.

    • With a bit of refactoring, this test could be even smaller (the launcher proxy classes could have a method to click an icon given a desktop id), but this is now perfectly readable and understandable within a few seconds of reading.

    Good docstrings

    Test docstrings are used to communicate to other developers what the test is supposed to be testing. Test Docstrings must:

  • Conform to href="http://www.python.org/dev/peps/pep-0008/">PEP8 and href="http://www.python.org/dev/peps/pep-0257/">PEP257 guidelines.
  • Avoid words like “should” in favor of stronger words like “must”.
  • Contain a one-line summary of the test.
    • Additionally, they should:
    1. Include the launchpad bug number (if applicable).

    Good Example:

    def test_launcher_switcher_next_keeps_shortcuts(self):
"""Launcher switcher next action must keep shortcuts after they've been shown."""

    Within the context of the test case, the docstring is able to explain exactly what the test does, without any ambiguity. In contrast, here’s a poorer example:

    Bad Example:

    def test_switcher_all_mode_shows_all_apps(self):
"""Test switcher 'show_all' mode shows apps from all workspaces."""

    The docstring explains what the desired outcome is, but without how we’re testing it. This style of sentence assumes test success, which is not what we want! A better version of this code might look like this:

    def test_switcher_all_mode_shows_all_apps(self):
"""Switcher 'show all' mode must show apps from all workspaces."""

    The difference between these two are subtle, but important.

    Test Readability

    The most important attribute for a test is that it is correct - it must test what’s it’s supposed to test. The second most important attribute is that it is readable. Tests should be able to be examined by themselves by someone other than the test author without any undue hardship. There are several things you can do to improve test readability:

    1. Don’t abuse the setUp() method. It’s tempting to put code that’s common to every test in a class into the setUp method, but it leads to tests that are not readable by themselves. For example, this test uses the setUp method to start the launcher switcher, and tearDown to cancel it:
    Bad Example:

    def test_launcher_switcher_next(self):
"""Moving to the next launcher item while switcher is activated must work."""
self.launcher_instance.switcher_next()
self.assertThat(self.launcher.key_nav_selection, Eventually(GreaterThan(0)))

    This leads to a shorter test (which we’ve already said is a good thing), but the test itself is incomplete. Without scrolling up to the setUp and tearDown methods, it’s hard to tell how the launcher switcher is started. The situation gets even worse when test classes derive from each other, since the code that starts the launcher switcher may not even be in the same class!

    A much better solution in this example is to initiate the switcher explicitly, and use addCleanup() to cancel it when the test ends, like this:

    Good Example:

    def test_launcher_switcher_next(self):
"""Moving to the next launcher item while switcher is activated must work."""
self.launcher_instance.switcher_start()
self.addCleanup(self.launcher_instance.switcher_cancel)
self.launcher_instance.switcher_next()
self.assertThat(self.launcher.key_nav_selection, Eventually(GreaterThan(0)))

    The code is longer, but it’s still very readable. It also follows the setup/action/test convention discussed above.

    Appropriate uses of the setUp() method include:

    • Initialising test class member variables.
    • Setting unity options that are required for the test. For example, many of the switcher autopilot tests set a unity option to prevent the switcher going into details mode after a timeout. This isn’t part of the test, but makes the test easier to write.
    • Setting unity log levels. The unity log is captured after each test. Some tests may adjust the verbosity of different parts of the Unity logging tree.
    1. Put common setup code into well-named methods. If the “setup” phase of a test is more than a few lines long, it makes sense to put this code into it’s own method. Pay particular attention to the name of the method you use. You need to make sure that the method name is explicit enough to keep the test readable. Here’s an example of a test that doesn’t do this:
    Bad Example:

    def test_showdesktop_hides_apps(self):
"""Show Desktop keyboard shortcut must hide applications."""
self.start_app('Character Map', locale='C')
self.start_app('Calculator', locale='C')
self.start_app('Text Editor', locale='C')
# show desktop, verify all windows are hidden:
self.keybinding("window/show_desktop")
self.addCleanup(self.keybinding, "window/show_desktop")
open_wins = self.bamf.get_open_windows()
for win in open_wins:
self.assertTrue(win.is_hidden)

    In contrast, we can refactor the test to look a lot nicer:

    Good Example:

    def test_showdesktop_hides_apps(self):
"""Show Desktop keyboard shortcut must hide applications."""
self.launch_test_apps()
# show desktop, verify all windows are hidden:
self.keybinding("window/show_desktop")
self.addCleanup(self.keybinding, "window/show_desktop")
open_wins = self.bamf.get_open_windows()
for win in open_wins:
self.assertTrue(win.is_hidden)

    The test is now shorter, and the launch_test_apps method can be re-used elsewhere. Importantly - even though I’ve hidden the implementation of the launch_test_apps method, the test still makes sense.

    1. Hide complicated assertions behind custom assertXXX methods or custom matchers. If you find that you frequently need to use a complicated assertion pattern, it may make sense to either:
  • Write a custom matcher. As long as you follow the protocol laid down by the testtools.matchers.Matcher class, you can use a hand-written Matcher just like you would use an ordinary one. Matchers should be written in the autopilot.matchers module if they’re likely to be reusable outside of a single test, or as local classes if they’re specific to one test.
  • Write custom assertion methods. For example:
    • def test_multi_key_copyright(self):
"""Pressing the sequences 'Multi_key' + 'c' + 'o' must produce '?'."""
self.dash.reveal_application_lens()
self.keyboard.press_and_release('Multi_key')
self.keyboard.type("oc")
self.assertSearchText("?")

    This test uses a custom method named assertSearchText that hides the complexity involved in getting the dash search text and comparing it to the given parameter.

    Prefer wait_for and Eventually to sleep

    Early autopilot tests relied on extensive use of the python sleep call to halt tests long enough for unity to change its state before the test continued. Previously, an autopilot test might have looked like this:

    Bad Example:

    def test_alt_f4_close_dash(self):
"""Dash must close on alt+F4."""
self.dash.ensure_visible()
sleep(2)
self.keyboard.press_and_release("Alt+F4")
sleep(2)
self.assertThat(self.dash.visible, Equals(False))

    This test uses two sleep calls. The first makes sure the dash has had time to open before the test continues, and the second makes sure that the dash has had time to respond to our key presses before we start testing things.

    There are several issues with this approach:
    1. On slow machines (like a jenkins instance running on a virtual machine), we may not be sleeping long enough. This can lead to tests failing on jenkins that pass on developers machines.
    2. On fast machines, we may be sleeping too long. This won’t cause the test to fail, but it does make running the test suite longer than it has to be.

    There are two solutions to this problem:

    In Tests

    Tests should use the Eventually matcher. This can be imported as follows:

    from autopilot.matchers import Eventually

    The Eventually matcher works on all attributes in a proxy class that derives from UnityIntrospectableObject (at the time of writing that is almost all the autopilot unity proxy classes).

    The Eventually matcher takes a single argument, which is another testtools matcher instance. For example, the bad assertion from the example above could be rewritten like so:

    self.assertThat(self.dash.visible, Eventually(Equals(False)))

    Since we can use any testtools matcher, we can also write code like this:

    self.assertThat(self.launcher.key_nav_selection, Eventually(GreaterThan(prev_icon)))

    Note that you can pass any object that follows the testtools matcher protocol (so you can write your own matchers, if you like).

    In Proxy Classes

    Proxy classes are not test cases, and do not have access to the self.assertThat method. However, we want proxy class methods to block until unity has had time to process the commands given. For example, the ensure_visible method on the Dash controller should block until the dash really is visible.

    To achieve this goal, all attributes on unity proxy classes have been patched with a wait_for method that takes a testtools matcher (just like Eventually - in fact, the Eventually matcher just calls wait_for under the hood). For example, previously the ensure_visible method on the Dash controller might have looked like this:

    Bad Example:

    def ensure_visible(self):
"""Ensures the dash is visible."""
if not self.visible:
self.toggle_reveal()
sleep(2)

    In this example we’re assuming that two seconds is long enough for the dash to open. To use the wait_for feature, the code looks like this:

    Good Example:

    def ensure_visible(self):
"""Ensures the dash is visible."""
if not self.visible:
self.toggle_reveal()
self.visible.wait_for(True)

    Note that wait_for assumes you want to use the Equals matcher if you don’t specify one. Here’s another example where we’re using it with a testtools matcher:

    key_nav_selection.wait_for(NotEquals(old_selection))

    Scenarios

    Autopilot uses the python-testscenarios package to run a test multiple times in different scenarios. A good example of scenarios in use is the launcher keyboard navigation tests: each test is run once with the launcher hide mode set to ‘always show launcher’, and again with it set to ‘autohide launcher’. This allows test authors to write their test once and have it execute in multiple environments.

    In order to use test scenarios, the test author must create a list of scenarios and assign them to the test case’s scenarios class attribute. The autopilot ibus test case classes use scenarios in a very simple fashion:

    Good Example:

    class IBusTestsPinyin(IBusTests):
"""Tests for the Pinyin(Chinese) input engine."""
scenarios = [
('basic', {'input': 'abc1', 'result': u'\u963f\u5e03\u4ece'}),
('photo', {'input': 'zhaopian ', 'result': u'\u7167\u7247'}),
('internet', {'input': 'hulianwang ', 'result': u'\u4e92\u8054\u7f51'}),
('disk', {'input': 'cipan ', 'result': u'\u78c1\u76d8'}),
('disk_management', {'input': 'cipan guanli ', 'result': u'\u78c1\u76d8\u7ba1\u7406'}),
]
def test_simple_input_dash(self):
self.dash.ensure_visible()
self.addCleanup(self.dash.ensure_hidden)
self.activate_ibus(self.dash.searchbar)
self.keyboard.type(self.input)
self.deactivate_ibus(self.dash.searchbar)
self.assertThat(self.dash.search_string, Eventually(Equals(self.result)))

    This is a simplified version of the IBus tests. In this case, the test_simple_input_dash test will be called 5 times. Each time, the self.input and self.result attribute will be set to the values in the scenario list. The first part of the scenario tuple is the scenario name - this is appended to the test id, and can be whatever you want.

    Important

    It is important to notice that the test does not change its behavior depending on the scenario it is run under. Exactly the same steps are taken - the only difference in this case is what gets typed on the keyboard, and what result is expected.

    Scenarios are applied before the test’s setUp or tearDown methods are called, so it’s safe (and indeed encouraged) to set up the test environment based on these attributes. For example, you may wish to set certain unity options for the duration of the test based on a scenario parameter.

    Multiplying Scenarios

    Scenarios are very helpful, but only represent a single-dimension of parameters. For example, consider the launcher keyboard navigation tests. We may want several different scenarios to come into play:

  • A scenario that controls whether the launcher is set to ‘autohide’ or ‘always visible’.
  • A scenario that controls which monitor the test is run on (in case we have multiple monitors configured).

    • We can generate two separate scenario lists to represent these two scenario axis, and then produce the dot-product of thw two lists like this:

    from autopilot.tests import multiply_scenarios
class LauncherKeynavTests(AutopilotTestCase):
hide_mode_scenarios = [
('autohide', {'hide_mode': 1}),
('neverhide', {'hide_mode': 0}),
]
monitor_scenarios = [
('monitor_0', {'launcher_monitor': 0}),
('monitor_1', {'launcher_monitor': 1}),
]
scenarios = multiply_scenarios(hide_mode_scenarios, monitor_scenarios)

    (please ignore the fact that we’re assuming that we always have two monitors!)

    In the test classes setUp method, we can then set the appropriate unity option and make sure we’re using the correct launcher:

    def setUp(self):
self.set_unity_option('launcher_hide_mode', self.hide_mode)
self.launcher_instance = self.launcher.get_launcher_for_monitor(self.launcher_monitor)

    Which allows us to write tests that work automatically in all the scenarios:

    def test_keynav_initiates(self):
"""Launcher must start keyboard navigation mode."""
self.launcher.keynav_start()
self.assertThat(self.launcher.kaynav_mode, Eventually(Equals(True)))

    This works fine. So far we’ve not done anything to cause undue pain.... until we decide that we want to extend the scenarios with an additional axis:

    from autopilot.tests import multiply_scenarios
class LauncherKeynavTests(AutopilotTestCase):
hide_mode_scenarios = [
('autohide', {'hide_mode': 1}),
('neverhide', {'hide_mode': 0}),
]
monitor_scenarios = [
('monitor_0', {'launcher_monitor': 0}),
('monitor_1', {'launcher_monitor': 1}),
]
launcher_monitor_scenarios = [
('launcher on all monitors', {'monitor_mode': 0}),
('launcher on primary monitor only', {'monitor_mode': 1}),
]
scenarios = multiply_scenarios(hide_mode_scenarios, monitor_scenarios, launcher_monitor_scenarios)

    Now we have a problem: Some of the generated scenarios won’t make any sense. For example, one such scenario will be (autohide, monitor_1, launcher on primary monitor only). If monitor 0 is the primary monitor, this will leave us running launcher tests on a monitor that doesn’t contain a launcher!

    There are two ways to get around this problem, and they both lead to terrible tests:

  • Detect these situations and skip the test. This is bad for several reasons - first, skipped tests should be viewed with the same level of suspicion as commented out code. Test skips should only be used in exceptional circumstances. A test skip in the test results is just as serious as a test failure.
  • Detect the situation in the test, and run different code using an if statement. For example, we might decode to do this:
    • def test_something(self):
# ... setup code here ...
if self.monitor_mode == 1 and self.launcher_monitor == 1:
# test something else
else:
# test the original thing.

    As a general rule, tests shouldn’t have assert statements inside an if statement unless there’s a very good reason for doing so.

    Scenarios can be useful, but we must be careful not to abuse them. It is far better to spend more time typing and end up with clear, readable tests than it is to end up with fewer, less readable tests. Like all code, tests are read far more often than they’re written.

    Do Not Depend on Object Ordering

    Calls such as select_many return several objects at once. These objects are explicitly unordered, and test authors must take care not to make assumptions about their order.

    Bad Example:

    buttons = self.select_many('Button')
save_button = buttons[0]
print_button = buttons[1]

    This code may work initially, but there’s absolutely no guarantee that the order of objects won’t change in the future. A better approach is to select the individual components you need:

    Good Example:

    save_button = self.select_single('Button', objectName='btnSave')
print_button = self.select_single('Button', objectName='btnPrint')

    This code will continue to work in the future.