Nw Test Optimization Consolidation

Consolidation Patterns (KNOWLEDGE)

Kind: KNOWLEDGE (reference). One trigger: "I have redundant tests — how do I collapse them without losing coverage" — consulted when the budget gate fires consolidation, or the paradigm-match rule routes here. Composed by nw-test-optimization.

Apply in this order. Each preserves coverage.

3.1 Parametrize Collapse

When N tests differ only by input value with the same assertion shape, collapse to one parametrized test. Failure granularity preserved by parameter ID.

3.2 Dict Iteration Collapse

When N parametrized tests assert independent membership/equality, collapse to one test iterating a dict and reporting all violations at once.

# BEFORE — 12 tests
@pytest.mark.parametrize("event,handler", [("RED", h1), ("GREEN", h2), ...])
def test_event_routes_to_handler(event, handler):
    assert ROUTING[event] is handler

# AFTER — 1 test, all violations reported
def test_event_routing_table_complete_and_correct():
    expected = {"RED": h1, "GREEN": h2, "COMMIT": h3, ...}
    assert ROUTING == expected

3.3 Fixture Scope Promotion

Read-only fixtures used by N tests can promote to module or session scope when independence is preserved (no shared mutable state). Speeds up wall time without changing behavior coverage.

@pytest.fixture(scope="module")  # was "function"
def loaded_skill_index():
    return SkillIndex.load_from(SKILLS_DIR)

Audit: tests using the fixture must not mutate it. If any test mutates, scope cannot promote.

3.4 xdist_group Tagging

When same-file tests benefit from a shared expensive fixture, add @pytest.mark.xdist_group("name") so the scheduler keeps them on the same worker. Fixture setup runs once per worker instead of once per test.

@pytest.mark.xdist_group("expensive_http_server")
class TestRemoteVersionService:
    # All methods share the HTTP server fixture, scheduled to one worker
    ...

3.5 Migration-Collapse Lifecycle

Regression nets from one-time migrations (rename, move, restructure) MUST collapse within 1 stable release after migration completion. Definition of "stable release":

• 1 release with the migration code green in CI for at least 7 days
• No follow-up bug reports referencing the migration during that window

After stabilization:

• Replace per-item parametrized tests with 1 single-iteration test reporting all violations at once
• Keep failure messages informative (set difference, dict diff)
• Document the collapse in commit body: refactor(tests): collapse {migration} regression net (315 → 3) — stable since {date}

3.6 Cross-Tier Deduplication

If tests/<file>.py and tests/<subdir>/<file>.py are byte-identical (md5-equal), delete the less canonical one. Canonical = the tier-correct location (unit under unit/, integration under integration/).

If two files are not byte-identical but assert the same handler/service through overlapping intent, merge into the canonical tier and delete the other.

3.7 Single-Lifecycle Consolidation

When N tests share an expensive setup/teardown lifecycle (subprocess install, container start, filesystem fixture build) AND each test asserts a distinct contract on the same post-setup state, collapse to one lifecycle, N assertions instead of N lifecycles × 1 assertion.

# BEFORE — 24 tests × ~6s lifecycle each = 152s wall-clock
class TestTutorialSetupScripts:
    def setup_method(self):
        self.workspace = build_tutorial_workspace()  # expensive
        run_setup_script(self.workspace)
    def test_creates_project_dir(self): assert (self.workspace / "project").is_dir()
    def test_creates_config_file(self): assert (self.workspace / ".nwave/config.json").exists()
    # ... 22 more independent assertions ...

# AFTER — 1 lifecycle, 24 assertions = 63s wall-clock (2.4× faster)
@pytest.fixture(scope="class")
def tutorial_workspace():
    workspace = build_tutorial_workspace()
    run_setup_script(workspace)
    return workspace

class TestTutorialSetupScripts:
    def test_creates_project_dir(self, tutorial_workspace):
        assert (tutorial_workspace / "project").is_dir()
    def test_creates_config_file(self, tutorial_workspace):
        assert (tutorial_workspace / ".nwave/config.json").exists()
    # ... 22 more, all reading the same workspace ...

Empirical anchor: tests/build/acceptance/test_tutorial_setup_scripts.py (commit defc07f0d, 2026-05-18): 152.81s → 62.87s, 2.4× faster, -90s.

Pre-conditions (HARD GATES):

• Setup is read-only for the assertions — no test mutates shared state. If even one test mutates, scope cannot promote (audit per §3.3).
• Failure granularity preserved: each assertion identifies WHAT failed (file/property/contract), not just "setup failed".
• Tests remain order-independent — pytest-randomly must not change outcomes (proves no hidden coupling).

Anti-pattern: do NOT collapse when assertions verify steps of a state-transition sequence (run A → assert, mutate B → assert, mutate C → assert). That is state-delta paradigm territory (§3.8), not single-lifecycle.

3.8 State-Delta Paradigm (cross-ref)

For tests that mutate user-observable state (installer, uninstaller, sync, hooks, settings.json — ~28% of suite), use the state-delta paradigm instead of per-assertion lifecycle: capture initial state once, apply operation, assert the delta (added/removed/modified) as a single matcher.

Honest gain: 13% compression / 17% wall-clock on the addressable subset (Ale 2026-05-05 revision). NOT universal — pure-function/AST/schema tests retain standard assertions (3-5× ceremony for zero gain otherwise).

See: nw-state-delta-paradigm skill (when present) and memory feedback_state_transition_test_paradigm for scope rules. Empirical anchor: Task #12 pilot (both slices).