Tests: Fill navigation fallback REST read-side empty stubs

[shail-mehta]

Trac ticket: #40538

What

Replaces the empty @doesNotPerformAssertions stubs for test_context_param() and test_get_items() in the navigation fallback REST API tests with real assertions.

Why

Per #40538, remaining read-side empty stubs should become real assertions. rest-navigation-fallback-controller.php has two claimable read-side cases. Write-side and prepare_item stubs are left alone pending #66073.

How

In WP_REST_Navigation_Fallback_Controller_Test:

• test_context_param() — OPTIONS /wp-block-editor/v1/navigation-fallback and assert no context arg
• test_get_items() — GET /wp-block-editor/v1/navigation-fallbacks and assert rest_no_route / 404 (no collection route)

Testing instructions

1. From the repo root, run:

node ./tools/local-env/scripts/docker.js run --rm php ./vendor/bin/phpunit --filter 'WP_REST_Navigation_Fallback_Controller_Test::test_context_param|WP_REST_Navigation_Fallback_Controller_Test::test_get_items'

2. Confirm both tests pass and are not reported as risky.

Use of AI Tools

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[lancewillett]

Please keep the OPTIONS assertions in test_context_param(), but leave test_get_items() as an annotated stub with a note that this controller has no collection operation.

The real route is the singleton /wp-block-editor/v1/navigation-fallback. Adding an s creates an unrelated, unregistered URL; its 404 does not exercise the navigation fallback controller. The ticket guidance allows documenting this unsupported operation.

The patch passes locally and CI is green; this request concerns the usefulness of the collection check.

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_{Adversarial review · gpt-6}

[shail-mehta]

I have applied changes in latest commit.

[lancewillett]

PR #13855 landed in https://core.trac.wordpress.org/changeset/64021