tests/project/test_isort_clean.py skips on every CI leg, invisibly to the dependency-gate guard

[JarryShaw]

Describe the bug

tests/project/test_isort_clean.py (added in #761) skips on every CI leg, and does it in a
form tests/_dependency_gates.py cannot see — so it is the third instance of exactly the failure
mode #745 was built to stop.

Reproduction

unit-tests.yml is the only workflow running pytest. Its three install lines are
.[test,DPKT,crypto,NGAP], .[test,Scapy,DPKT,cli] and .[test,Scapy,DPKT,crypto,cli,NGAP];
isort is in none of them and is absent from the test extra, from Pipfile's [dev-packages],
and from pyproject.toml entirely. With isort blocked at import:

setUpClass (tests.project.test_isort_clean.TestIsortIsCleanOnThePackage) ... skipped
Ran 0 tests in 0.000s
OK (skipped=1)

The regression it exists to catch passes green.

Expected behavior

Either the test runs on at least one CI leg, or its gate is visible to the dependency-gate
machinery and explicitly excluded with a stated reason.

Additional context

The guard reads unittest.skipUnless decorators; this raises SkipTest inside setUpClass, so
flag_requirements() never sees it — tests/test_tier_guard.py is 84 passed / 485 subtests green
with the hole open. The cited precedent is not equivalent: TestYAMLAgreesWithTheScanner skips
with a stated fallback, so something always runs. Here nothing does.

Blocked on #755, which owns tests/test_tier_guard.py and .github/workflows/unit-tests.yml.
Adding a visible HAS_ISORT gate would correctly turn the guard red until isort is on an install
line, so both files have to move together. Found in the cross-review of #761.

[JarryShaw]

Still blocked, but the blocker has moved. #755 has merged, so tests/test_tier_guard.py and .github/workflows/unit-tests.yml are free — but the fix also needs tests/project/test_isort_clean.py, which a live worker owns for #765 and #767. Adding a visible HAS_ISORT gate there would correctly turn the dependency-gate guard red until isort is on a pytest install line, so the test file and the workflow have to move together.

Unblocks when the #765/#767 PR lands.

[JarryShaw]

Blocker moved again, and #766 stays blocked — but on a different PR.

#773 merged as 110381b63, so tests/project/test_isort_clean.py is free at last. But the remaining half of this fix needs .github/workflows/unit-tests.yml, tests/test_tier_guard.py and pyproject.toml — to put isort on a pytest install line, so that a visible HAS_ISORT gate does not turn the dependency-gate guard red. All three are owned by #774 (fix-738-vendor-deps-engine-tests, head 1b63e9899, review: pending, worker live). Two agents editing unit-tests.yml at once means the later write wins silently, which is exactly the failure this label exists to prevent.

Checkable blocker: #774 merged. Then the fix goes out as one PR — the HAS_ISORT gate, the isort install line, and whatever tests/_dependency_gates.py entry the guard then wants.

[JarryShaw]

Blocker moves from #774 to #779, and stays a real one. #774 merged at 12:15:52Z as 35a79016b, so the workflow and the guard are free of that hold — but this fix and #779 both need tests/_dependency_gates.py, and #779 is the one that adds the MODULE_PROVIDERS machinery a visible HAS_ISORT gate will lean on. Two agents editing that file at once means the later write wins silently.

Checkable blocker: #779 merged. Then the HAS_ISORT gate, the isort install line in .github/workflows/unit-tests.yml, and whatever DEPENDENCY_GATE_EXCLUSIONS entry the guard then wants all go out together.

[JarryShaw]

Unblocked — #782 merged at 13:17:38Z as 0419c1c97, so tests/_dependency_gates.py is free and its MODULE_PROVIDERS machinery is on main. main is now 0419c1c97.

What landed that this fix can lean on: MODULE_PROVIDERS['mypy'] exists as precedent for a lint-tier tool, _top_level_providers replaces the three bare subscripts so an unmapped module now names itself and the table to add it to instead of raising a bare KeyError, and DEPENDENCY_GATE_EXCLUSIONS gained an entry whose rationale is the same shape this one will need — a gate that is dark on the pytest jobs because the tool is installed by lint.yml, which runs no pytest at all.

Dispatching: the HAS_ISORT gate in tests/project/test_isort_clean.py, the isort install line in .github/workflows/unit-tests.yml or an exclusion explaining why there is none, and whatever tests/_dependency_gates.py entry the guard then wants.