polylith-migrate-refactor-tests

Testing & Quality

[Internal sub-skill of `polylith-migrate-orchestrator`. Do not load directly — load `polylith-migrate-orchestrator` first, which drives all phases.] Restructure unit tests to align with the workspace's Polylith theme.

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Skill: polylith-migrate-refactor-tests

Goal

Restructure unit tests so they live next to the brick they test, following the workspace's Polylith theme (loose or tdd).

Scope

Unit tests only. Integration tests typically stay in a shared location (e.g., test/integration/ or test/<project>/integration/). Do not redistribute them across bricks.
Structure only. Reorganize test files and update imports/mock patch strings. Do not rewrite test logic or fixtures unless an import/path change makes it strictly necessary.

Shared test helpers & the namespace-merge hazard (read before moving)

Two real traps when moving unit tests next to their bricks:

Shared test-support packages stop resolving. If tests import shared helpers/fixtures by package (e.g. from <svc>_service.helpers import …, from <svc>_service.fixtures import …), those resolve today only because the service test dir sits on sys.path (pytest inserts the topmost non-package dir). Once a test moves to test/components/<TARGET_TOP_NS>/<comp>/ (no __init__.py), pytest inserts the leaf test dir instead, and the shared import breaks.
Do NOT "fix" it by adding test/ to pythonpath. That makes test/<…>/<TARGET_TOP_NS>/<brick>/ directories merge into the real <TARGET_TOP_NS> namespace and collide with components/<TARGET_TOP_NS>/<brick> / bases/<TARGET_TOP_NS>/<brick> — an ambiguous, hard-to-debug namespace package.

Two sanctioned layouts — pick one

Per-brick (the target table below). Use it after making shared helpers reachable without putting test/ on the path: convert them to conftest.py fixtures (pytest injects fixtures with no import), or move pure helper functions to an on-path support location. Unit tests then live under test/<theme>/<TARGET_TOP_NS>/<brick>/.
Workspace-level service dir. Keep the project's tests under a single test/<svc>_service/ directory (the importable, valid-package name that polylith-migrate-prepare-project created). Shared helpers stay co-located and importable. Choose this when converting helpers to fixtures isn't worth it; record the choice in state.md. This still satisfies "tests at workspace level".

If unsure, the workspace-level service dir is the lower-risk default.

Inputs

From migration/<PROJECT>/state.md:

TARGET_TOP_NS
RUN_TEST_CMD (will be updated by this skill)
RUN_LINT_CMD, RUN_TYPECHECK_CMD (optional)

From migration/<PROJECT>/manifest.md:

List of all bricks (bases and components) with their module maps.

From workspace.toml:

[tool.polylith.structure].theme (loose or tdd).

From test/:

Current test directory structure.

All inputs from state.md are assumed to satisfy the validation rules in polylith-migrate-discover (### Validation rules). Validate before proceeding.

Target layout

Theme	Test path for a base	Test path for a component
`loose`	`test/bases/<TARGET_TOP_NS>/<base>/test_*.py`	`test/components/<TARGET_TOP_NS>/<component>/test_*.py`
`tdd`	`bases/<base>/test/<TARGET_TOP_NS>/<base>/test_*.py`	`components/<component>/test/<TARGET_TOP_NS>/<component>/test_*.py`

Steps

1. Classify each unit test file

For each test_*.py under the current test root:

Read its import statements and mock.patch("...") strings.
Identify the primary brick under test — usually the one most imported or the one mock-patched. Tie-break by file name (test_user_handler.py → <user_handler base or component>).
Record the classification in a table you keep in scratch (do not commit a separate file for this — it's transient):

Test file	Primary brick	Target path

If a test exercises 2+ bricks at integration level, classify it as integration and move it to test/integration/ instead.

2. Move test files

Create the target directories per the theme matrix above.
Move each test_*.py to its brick's test directory.
For each conftest.py:
- Brick-scoped fixtures (referenced only by tests under one brick) → move to that brick's test directory.
- Workspace-shared fixtures (cross-brick) → keep one test/<TARGET_TOP_NS>/conftest.py or test/conftest.py.

3. Update imports and mock patch strings

Update any from tests.<x> imports that survived to the new layout.
Update mock.patch("<old.path>") strings. Brick reshuffling earlier in the migration may have changed where the patched symbol now lives — use grep to locate the target symbol's new path and align the patch string. Patching a wrong path silently succeeds and the test will pass for the wrong reason — verify by intentionally breaking the target function and checking that the test fails.

4. Update `RUN_TEST_CMD`

Set RUN_TEST_CMD in state.md to a command that collects from the new test root (typically <POLY_CMD_PREFIX_RUN> pytest test/ for loose, or per-brick collection for tdd).
Verify the test count after the move equals the baseline recorded in polylith-migrate-discover. A drop in collected tests means files were lost or pytest discovery is misconfigured.

Verify

RUN_TEST_CMD succeeds and collects the same number of tests as the baseline from polylith-migrate-discover.
If set, RUN_LINT_CMD succeeds.
POLY_CMD_PREFIX check is still green.

Common failure modes

Symptom	Likely cause	Remediation
`pytest` collects fewer tests than before	The old test root is no longer on `pytest`'s path; or duplicate `conftest.py` files silently shadow each other.	Update `[tool.pytest.ini_options].testpaths` (or pass paths explicitly in `RUN_TEST_CMD`). Run `pytest --collect-only` and diff against baseline collection.
`fixture '<name>' not found`	The fixture was in a `conftest.py` you moved into a brick's test dir; tests in another brick can no longer see it.	Either move the fixture up to a higher-scope `conftest.py`, or duplicate it (only if cheap). Don't import fixtures across `conftest.py` files.
Tests pass but assert nothing useful (`mock.patch` no longer hits anything)	Patch string still points at the pre-migration module path.	Re-derive the patch path: `<TARGET_TOP_NS>.<brick_name>.<module>.<symbol>`. Validate by deliberately breaking the patched function and confirming the test fails.
`ImportError: cannot import name 'fixture_<x>'` from `conftest.py`	A `conftest.py` `import`s a moved test helper module that didn't follow it.	Move the helper next to the new `conftest.py`, or import it from its new brick path.
Tests for moved code suddenly find themselves under a brick name that doesn't match their content	Misclassification in step 1.	Re-read the test's imports — the brick most imported is the one that owns the test. Move and update.
`ModuleNotFoundError: No module named '<svc>_service'` after moving a test to `test/<theme>/<TARGET_TOP_NS>/<brick>/`	Shared test-support package is no longer on `sys.path`.	Use a sanctioned layout (above): convert the helpers to conftest fixtures, or keep tests in the workspace-level `<svc>_service/` dir. Do not add `test/` to `pythonpath` (namespace merge with the real bricks).
Verification fails and you can't quickly diagnose	Phase commit not yet made.	`git reset --hard HEAD` to roll back to the previous phase's commit and consult the user.

Commit

After verification passes, commit this phase to the migration branch:

git add -A && git commit -m "migrate(<PROJECT>): phase <N> — refactor-tests"

Substitute <PROJECT>, <N>, and <phase-name> from state.md and the orchestrator's phase table. Do not proceed to the next phase without a clean commit — the per-phase commit is the rollback point for the next phase's failure-mode tables.