Add unit tests for the FAB app-init extensions

[ShousenZHANG]

Five of the seven providers/fab/src/airflow/providers/fab/www/extensions/ modules are listed in OVERLOOKED_TESTS with no tests at all, and create_app() reaches all five while building the Flask app: configure_manifest_files at www/app.py:113 and init_api_auth at :114, then init_error_handlers at :118, init_plugins at :127 (only when enable_plugins), init_jinja_globals at :130 and init_wsgi_middleware at :131 inside the app_context opened at :116. Nothing in create_app catches, so a failure in any of them stops the app from starting; a silent behaviour change in init_wsgi_middleware or init_jinja_globals instead alters what gets served.

Grouped into one PR per the request on #35442 — "Batch a provider's worth of missing test modules into a single PR instead."

What the tests pin

module	pinned behaviour
init_wsgi_middlewares	the five [fab] proxy_fix_x_* options set to five distinct values, so a mix-up between the five near-identical ProxyFix keyword arguments fails; wsgi_app untouched when the option is off
init_security	the comma split and per-entry strip, import order, the default backend, and ImportError → AirflowException
init_jinja_globals	the three default_timezone branches incl. the non-callable guard, hostname redaction when [fab] expose_hostname is off, the four navbar colours, and the two opposite globals driven by enable_plugins
init_manifest_files	the dist/ prefixing, the fallback to the raw filename when the manifest is missing or the key unknown, the debug-mode re-read
init_views	view not forwarded twice for named views, add_view_no_menu for unnamed ones, the named-view-without-a-view log, blueprint registration, the 500/404 handler pair

One behaviour is recorded rather than asserted as correct: an empty [fab] auth_backends makes init_api_auth call import_module(""), which raises ValueError, and the function's except ImportError does not catch it — so it escapes as a bare ValueError instead of the AirflowException every other bad backend produces. The test documents that; fixing it belongs in a change to the module, not here.

Mutation results

Assertion count says nothing about whether a test can fail, so each of the five modules was broken one line at a time. 22 of 22 mutations are caught:

• init_wsgi_middlewares (4/4) — x_host reading PROXY_FIX_X_PORT; dropping the x_prefix= keyword; inverting the ENABLE_PROXY_FIX guard; hardcoding x_for=1
• init_security (4/4) — dropping .strip(); swallowing the ImportError; not appending to app.api_auth; widening except ImportError to except Exception
• init_jinja_globals (6/6) — not upper-casing utc; dropping the non-callable local_timezone guard; inverting the hostname redaction; swapping two navbar colours; un-inverting disable_nav_bar; letting the version lookup raise
• init_manifest_files (4/4) — dropping the dist/ prefix; narrowing the bare except; removing the debug re-read; ignoring the manifest lookup
• init_views (4/4) — forwarding the whole view dict to add_view; using add_view for unnamed views; swapping the 500/404 handlers; skipping blueprint registration

Scope and conflicts

This clears 5 of the 7 fab/www/extensions exemptions. The two left are init_appbuilder (615 lines, needs a real AirflowAppBuilder) and init_session, which #72825 already covers.

Two things a reviewer should know:

• Add FAB option to log users out after a maximum session lifetime #72825 and this PR both create providers/fab/tests/unit/fab/www/extensions/__init__.py — the directory does not exist on main, so whichever lands second gets an add/add conflict. Happy to rebase onto Add FAB option to log users out after a maximum session lifetime #72825; say the word and I will.
• The OVERLOOKED_TESTS removal is currently unenforced. test_project_structure.py:227 does current_test_files.intersection(OVERLOOKED_TESTS), comparing a set[Path] against a list[str], so that assertion can never fire. I removed the five lines because the list should reflect reality, not because CI would otherwise fail. Reject stale provider test exemptions #71985 already fixes that comparison and prunes stale entries, so I have not touched it.

init_plugins' pre-3.1/pre-3.2 branches are unreachable on main (AIRFLOW_V_3_1_PLUS and AIRFLOW_V_3_2_PLUS are both true) and are not covered; TestInitPlugins carries a matching skipif.

Verification

• pytest providers/fab/tests/unit/fab/www/extensions/ — 27 passed
• pytest airflow-core/tests/unit/always/test_project_structure.py — 10 passed, 1 pre-existing xfail
• ruff check and ruff format --check — clean
• prek run --files <the 8 changed files> — 0 failed

Was generative AI tooling used to co-author this PR?

• Yes — Claude Code

Generated-by: Claude Code following the guidelines

The tests were written by an AI assistant. I checked the call sites in www/app.py, ran the 22 mutations above to confirm every test can actually fail, and ran the commands under Verification.

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[vincbeck]

The issue has been closed, no need to add all these tests