t453: Write unit tests for Checkout class

[superdav42]

Summary

• Adds 171 PHPUnit tests for WP_Ultimo\Checkout\Checkout covering all public methods and key protected methods via reflection
• Tests are resilient to both canonical and worktree code differences (e.g. discount_code key presence)
• All 171 tests pass, 1 skipped (environment-dependent customer lookup)

Coverage areas

Area	Tests
Singleton	2
contains_auto_submittable_field	8
get_auto_submittable_fields	2
is_existing_user	2
handle_display_name	5
request_or_session	5
Step navigation (is_first_step, is_last_step, get_next_step_name)	10
Email verification status	5
errors property	2
should_process_checkout	3
validation_rules	9
should_collect_payment	5
get_thank_you_page	1
get_checkout_variables	20+
cleanup_expired_drafts	4
can_user_cancel_payment	3
validate	7
get_validation_rules	8
create_draft_payment / save_draft_progress	4
get_js_validation_rules	7
maybe_display_checkout_errors	2
get_checkout_from_query_vars	4
get_site_meta_fields	3
handle_customer_meta_fields	3
maybe_create_customer	6
maybe_create_membership	2
maybe_create_payment	4
maybe_create_site	3
setup_checkout	8
handle_cancel_payment	3
process_order	3
process_checkout	1
add_rewrite_rules / register_scripts	2

Runtime Testing

• Testing level: unit-tested
• Risk classification: low (test files only)
• Dev environment: WordPress multisite test suite (/tmp/wordpress-tests-lib)
• Result: 171 tests pass, 1 skipped

Closes #555

Summary by CodeRabbit

• Tests
  • Expanded test coverage for Checkout functionality, including setup flows, payment cancellation, error handling, and validation rules.
  • Enhanced test isolation to ensure reliable and independent test execution.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 51d7d94e-ae89-452d-8b42-7a2e70869b43

📥 Commits

Reviewing files that changed from the base of the PR and between 055e5e1 and fa99418.

📒 Files selected for processing (1)

• tests/WP_Ultimo/Checkout/Checkout_Test.php

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📝 Walkthrough

Walkthrough

The PR adds comprehensive unit test coverage for the Checkout class, including setup initialization, payment cancellation handling, getter methods, validation rules, session handling, and error path scenarios. Test setup enhances database isolation through user and customer deletion.

Changes

Cohort / File(s)	Summary
Checkout Unit Tests tests/WP_Ultimo/Checkout/Checkout_Test.php	Adds 2779 lines of test coverage for Checkout class including setup state verification, payment cancellation behavior, getter methods with branch coverage, validation rules, session management, reflection-based protected method testing, error path handling, and improved test isolation via database cleanup.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~50 minutes

Possibly related PRs

• PR #372: The expanded Checkout tests covering setup, payment cancellation, variables retrieval, and error paths directly validate the functional changes to checkout/cart/payment and class-checkout.php behavior.
• PR #367: Directly modifies the same test file (tests/WP_Ultimo/Checkout/Checkout_Test.php) with related Checkout test additions and setup/teardown enhancements.

Poem

🐰 A burrow of tests, now thoroughly sewn,
Each path through Checkout is carefully known,
Setup, cancellation, validation so bright,
Error cases tested from left to right,
Coverage takes flight, our goals now full-grown! ✨

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feature/t453-checkout-coverage

---

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[github-actions]

🔨 Build Complete - Ready for Testing!

📦 Download Build Artifact (Recommended)

Download the zip build, upload to WordPress and test:

• Build: ultimate-multisite
• ⬇️ Download from GitHub Actions
• ⬇️ Download without Github Account (nightly.link)

🌐 Test in WordPress Playground (Very Experimental)

Click the link below to instantly test this PR in your browser - no installation needed!
Playground support for multisite is very limitied, hopefully it will get better in the future.

🚀 Launch in Playground

Login credentials: admin / password

[github-actions]

Performance Test Results

Performance test results for 15a52a8 are in 🛎️!

URL: /

Run	DB Queries	Memory	Before Template	Template	WP Total	LCP	TTFB	LCP - TTFB
0	57	36.39 MB	293.50 ms	103.50 ms	397.00 ms	490.05 ms	410.80 ms	79.55 ms
1	57	36.39 MB	293.00 ms	102.00 ms	395.50 ms	489.50 ms	409.75 ms	79.85 ms

[github-actions]

🔨 Build Complete - Ready for Testing!

📦 Download Build Artifact (Recommended)

Download the zip build, upload to WordPress and test:

• Build: ultimate-multisite
• ⬇️ Download from GitHub Actions
• ⬇️ Download without Github Account (nightly.link)

🌐 Test in WordPress Playground (Very Experimental)

Click the link below to instantly test this PR in your browser - no installation needed!
Playground support for multisite is very limitied, hopefully it will get better in the future.

🚀 Launch in Playground

Login credentials: admin / password