test: enforce the test layout and hold the line coverage

[YvesCesar]

The conventions the suite follows were kept by review only: a new class could land without a test, and a test could outlive the file it was named after. This adds the two checks that keep them, on top of the Playwright suite from #12 (hence the base branch; it retargets to main once #9, #10, #11 and #12 are merged).

The two files that had no test

src/Autoloader.php and src/Github/WebhookDecision.php were the only source files with no test named after them, so they come first — the layout check would fail on them otherwise.

• tests/Unit/AutoloaderTest.php — the loader lands in the stack, every class of the plugin is loaded from the file named after it, a class of another project is left alone, and a class with no file is not an error.
• tests/Unit/Github/WebhookDecisionTest.php — the four answers a delivery can get, what each one carries, and the LogicException the three that are not a deploy throw when asked for a workflow run. Its lines were already exercised through WebhookGateTest, which is exactly why it was easy to miss.

The layout check

tests/Unit/StructureTest.php reads the repository instead of a list kept by hand (tests/Support/PluginFiles.php) and fails in both directions:

• a file of the plugin with no test named after it — src/X.php wants tests/Unit/XTest.php or tests/Integration/XTest.php, includes/foo-bar.php wants tests/Integration/Includes/FooBarTest.php, and the main file wants tests/Integration/LibresignWpCustomizationsTest.php;
• a test named after a file that does not exist, including .spec.ts under tests/E2E/.

The failure names both paths, so a rename that breaks the mirror says which file to move:

src/Github/Orphan.php is not covered by tests/Unit/Github/OrphanTest.php or tests/Integration/Github/OrphanTest.php.
tests/Unit/Account/StrayTest.php does not cover src/Account/Stray.php.

The coverage floor

composer coverage runs the suite with Xdebug collecting coverage and hands the clover report to bin/coverage-gate.php, which compares it with coverage-floor.txt — today 65.33, the line coverage of libresign-wp-customizations.php, includes/ and src/ as it stands.

The floor only ever goes up. Coverage below it fails; coverage a full point above it fails too, printing the number to write in the file. A change that covers more raises the floor in the same commit, and coverage that quietly drains away between releases is not possible.

Line coverage: 65.33% (floor 65.33%).
Line coverage fell to 62.10%, below the floor of 65.33%. Cover what the change left uncovered.
Line coverage rose to 66.40%, above the floor of 65.33%. Raise it: echo 66.40 > coverage-floor.txt

composer ci now ends in coverage instead of test, so one command still runs everything CI runs. The Tests workflow gains a Coverage job on PHP 8.3 with Xdebug — the same driver as the container, so the number does not move between a local run and CI.

Verification

composer ci is green: no lint, PHPCS or PHPStan findings, 299 PHPUnit tests (up from 239), and the gate at 65.33%. The layout check was confirmed against a stray file and a stray test, the output above, and all four outcomes of the gate — at the floor, below it, above it, and a floor file that does not hold a number.

[vitormattos]

The implementation looks good to me now.