test(api): improve API class test coverage

[superdav42]

Task t484

Improve test coverage for inc/class-api.php.

Current coverage: 6.6% (199 uncovered statements)
Target: ≥80% coverage

Acceptance Criteria

• PHPUnit tests written for API class
• Coverage reaches ≥80% for this file
• All tests pass in CI (PHP 8.2, 8.3, 8.4, 8.5)
• No regressions in existing test suite

How

• Create test file at tests/unit/inc/
• Mock WordPress REST API functions
• Test endpoint registration and request handling

[superdav42]

Implementation Complete — PR #591 merged

What was done

• Expanded tests/WP_Ultimo/API_Test.php from 3 stub tests to 55 comprehensive PHPUnit tests
• All 13 public methods in inc/class-api.php now have dedicated test coverage
• Coverage target of ≥80% achieved (up from 6.6%)

Testing Evidence

• Testing level: unit-tested
• PHP versions: 8.2 ✅ 8.3 ✅ 8.4 ✅ 8.5 ✅ (all pass in CI)
• Local run: 55 tests, exit code 0
• Code Quality: pass | PHP Lint: pass | CodeRabbit: pass

Key decisions

• auth() tests use output buffering to handle wp_send_json → wp_die in test env (same pattern as other test files)
• check_authorization() tests clean up $_SERVER['PHP_AUTH_USER']/PHP_AUTH_PW in all paths to avoid test pollution
• register_routes() tests use setExpectedIncorrectUsage('register_rest_route') per project convention
• maybe_bypass_wp_auth() tests set $_SERVER['REQUEST_URI'] to simulate wu-namespace routes

Files changed

• tests/WP_Ultimo/API_Test.php — 822 lines added, 10 lines removed (replaced stub tests with comprehensive suite)

Blockers

• None

Follow-up needs

• None — all acceptance criteria met