test(admin): write unit tests for Edit_Admin_Page base class

[superdav42]

Task t479

File: inc/admin-pages/class-edit-admin-page.php
Current coverage: 2.8%
Uncovered statements: 375
Estimated time: ~4h

Write unit tests for Edit_Admin_Page base class to reach >=80% coverage.

Acceptance Criteria

• Edit_Admin_Page coverage reaches >=80%
• All new tests pass in CI
• No regressions in existing tests

Context

Part of the unit test coverage improvement initiative. See TODO.md t479.

[superdav42]

Implementation Complete

What was done:

• Added tests/WP_Ultimo/Admin_Pages/Edit_Admin_Page_Test.php with 59 unit tests for the Edit_Admin_Page abstract base class
• Created Test_Edit_Admin_Page concrete subclass that exposes protected methods as public wrappers for direct testing
• Implemented notices singleton reset between tests via reflection to prevent cross-test contamination

Coverage achieved:

• Statement coverage: 85.97% (331/385 statements) — up from 2.8%
• Method coverage: 95.65% (22/23 methods)
• Only output() excluded — requires wu_wrap_use_container() unavailable in unit test environment

Testing Evidence:

• Testing level: unit-tested
• Risk classification: Low (test files only, no production code changes)
• 59 tests pass, 1 skipped (DB-dependent edit mode test), 0 failures
• All PHP versions (8.2, 8.3, 8.4, 8.5) pass in CI
• No regressions in existing 218 admin page tests

Key decisions:

• Used Discount_Code as the backing model (lightweight, no side-effects on construction)
• Tested handle_save/handle_delete error paths via mocks (success paths call wp_safe_redirect + exit)
• Meta box callbacks are executed directly to cover the closure code inside widget registration methods

Files changed:

• tests/WP_Ultimo/Admin_Pages/Edit_Admin_Page_Test.php — new test file (1328 lines, 59 tests)

Merged in: PR #580