[wp-trac] [WordPress Trac] #53011: Tests: review all setUp() and tearDown()

[WordPress Trac]

#53011: Tests: review all setUp() and tearDown()
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 Reporter:  jrf                                  |      Owner:  (none)
     Type:  task (blessed)                       |     Status:  new
 Priority:  normal                               |  Milestone:  Awaiting
                                                 |  Review
Component:  Build/Test Tools                     |    Version:  trunk
 Severity:  normal                               |   Keywords:
  Focuses:  docs, performance, coding-standards  |
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 The `setUpBeforeClass()`, `setUp()`, `tearDown()` and
 `tearDownAfterClass()` (and the WP test suite native variants of these)
 methods in test classes are used to set up fixtures which will be used by
 all tests in the test class.

 Also see: https://phpunit.readthedocs.io/en/9.5/fixtures.html

 For tests to properly be able to test just and only that which is being
 tested, we need to make sure that changes to the "global state" are undone
 after each test.

 This includes:
 * Changes to variables in `$GLOBALS`, changes to global variables via
 `global $var_name`.
 * Changes to superglobals, like `$_GET`, `$_POST` or `$_REQUEST`.
 * Filters being hooked or ''un''hooked to WordPress using `add_filter()`,
 `remove_filter()`, `add_action()`, `remove_action()` (and all their
 variations) calls in `setUp()` methods - or in the tests themselves.
 * Changes in the file system - file being created by a test should be
 deleted after the test.
 * And more contentiously: changes in the database ought to be undone after
 a test as well. This doesn't mean that any posts being created for a test
 and only being used by that test need to be deleted, but it does mean that
 any schema changes, any new tables created etc ''should'' be undone after
 the test.

 At this time, the WP Core test suite does not consistently "undo" changes
 to the global state for each test, as @hellofromTonya and me found while
 reviewing tests for an unrelated patch.

 We would like to recommend a full review of the test suite for best
 practices regarding global state resetting after each test.

 Note: if a "reset" action is being done within the code of a test
 ''function'', it may not get executed when the tests fails. To that end,
 these type of "reset"s should generally be done in the `tearDown()`, even
 when they only apply to one test in the test class.
 The "reset", in that case, should be accompanied by a comment pointing to
 the test to which it applies.

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Ticket URL: <https://core.trac.wordpress.org/ticket/53011>
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