tests: replace function-scoped helper fixtures with TestHelper

[snejus]

• Test setup was consolidated into shared helper classes instead of using local helper fixtures.
• test/library/test_migrations.py now uses MigrationTestHelper to provide one common migration harness, with each test class defining only the legacy state and migration it needs.
• Plugin tests in test/plugins/test_fuzzy.py, test/plugins/test_missing.py, and test/plugins/utils/test_playcount.py now rely on shared helpers like PluginTestHelper and TestHelper for common setup.

Note: I kept these fixtures in these files

• test_query.py
• plugins/test_random.py
• plugins/test_aura.py
• plugins/test_lyrics.py

because they intentionally use a higher scope, for example in test_query.py:

@pytest.fixture(scope="class")
def helper():
    helper = TestHelper()
    helper.setup_beets()

    yield helper

    helper.teardown_beets()

Using this setup pattern in test_query.py significantly improved testing durations.

Architecture impact

• Test infrastructure now follows a clearer base-class pattern for shared setup.
• Migration tests cleanly separate 'prepare old state' from 'run migration and verify result'.
• Plugin tests now use the same setup path, which makes new tests easier to add and keeps test structure more consistent across files.

High-level outcome

• Less duplicated fixture boilerplate.
• More consistent and easier-to-read test architecture.
• Tests stay focused on behavior being verified, which should make maintenance and future extension simpler.

[github-actions]

Thank you for the PR! The changelog has not been updated, so here is a friendly reminder to check if you need to add an entry.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.72%. Comparing base (7de08ba) to head (2ad2368).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6709      +/-   ##
==========================================
+ Coverage   74.51%   74.72%   +0.21%     
==========================================
  Files         162      162              
  Lines       20820    20820              
  Branches     3298     3298              
==========================================
+ Hits        15514    15558      +44     
+ Misses       4549     4505      -44     
  Partials      757      757              

see 2 files with indirect coverage changes

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[Copilot]

Pull request overview

grug see PR make test setup less copy-paste. instead of local helper fixtures per file, tests now inherit shared helper classes (TestHelper/PluginTestHelper) and migration tests get one common harness.

Changes:

• swap function-scoped helper fixtures for TestHelper / PluginTestHelper base classes in plugin tests
• add MigrationTestHelper harness so each migration test only defines legacy setup + migration under test
• adjust playcount tests to use class-based helper + explicit log fixture injection

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
test/plugins/utils/test_playcount.py	move from helper fixture to TestHelper inheritance; pass logger via fixture
test/plugins/test_missing.py	use shared PluginTestHelper (plus IO mixin) for missing plugin CLI tests
test/plugins/test_fuzzy.py	use PluginTestHelper for fuzzy plugin tests; remove local helper fixture
test/library/test_migrations.py	introduce MigrationTestHelper and refactor migrations tests onto shared harness