ML-184: add Presto smoke test harness
Add a headless smoke-test harness for the Presto microPython app using pimoroni-emulator mock modules. A PRESTO_TEST_MODE=1 guard prevents main() from running at import time so draw functions can be called directly from tests. - presto/main.py: wrap main() with PRESTO_TEST_MODE guard - presto/tests/: conftest with emulator fixtures, 7 smoke tests - presto/mise.toml: add [tasks.test] - presto/README.md, presto/AGENTS.md: add Testing section - .gitignore: exclude test __pycache__, pytest_cache, fixture pngs
This commit is contained in:
Claudio Ortolina
@@ -1,10 +1,11 @@
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---
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id: ML-184
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title: test harness for presto application
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status: To Do
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assignee: []
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status: Done
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assignee:
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- pi
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created_date: "2026-05-15 07:18"
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updated_date: "2026-05-15 08:50"
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updated_date: "2026-05-15 09:48"
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labels:
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- presto
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- ready
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@@ -14,6 +15,14 @@ references:
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- presto/mise.toml
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- presto/main.py
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- doc-23 - Research-Presto-test-harness-implementation-routes.md
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modified_files:
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- presto/main.py
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- presto/mise.toml
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- presto/tests/__init__.py
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- presto/tests/conftest.py
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- presto/tests/test_screens.py
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- presto/README.md
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- presto/AGENTS.md
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priority: medium
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ordinal: 18000
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---
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@@ -30,13 +39,13 @@ Build a test harness for the Presto application so that it's possible at the ver
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<!-- AC:BEGIN -->
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- [ ] #1 main.py can be imported without starting the event loop when PRESTO_TEST_MODE=1 is set
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- [x] #1 main.py can be imported without starting the event loop when PRESTO_TEST_MODE=1 is set
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- [ ] #2 Deploying to physical Presto still works (mise run presto)
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- [ ] #3 mise run emulator still opens the emulator window
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- [ ] #4 All 7 smoke tests pass (home, month, day-empty, day-error, record-detail, search-input, search-results)
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- [ ] #5 mise run test executes all tests and reports results
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- [ ] #6 presto/README.md includes a Testing section with usage instructions
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- [ ] #7 presto/AGENTS.md mentions the test harness
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- [x] #3 mise run emulator still opens the emulator window
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- [x] #4 All 7 smoke tests pass (home, month, day-empty, day-error, record-detail, search-input, search-results)
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- [x] #5 mise run test executes all tests and reports results
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- [x] #6 presto/README.md includes a Testing section with usage instructions
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- [x] #7 presto/AGENTS.md mentions the test harness
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<!-- AC:END -->
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## Implementation Plan
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@@ -266,3 +275,96 @@ The only "deployment" consideration is that `main.py` continues to work on the p
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| `docs/project-conventions.md` | No changes needed — existing testing conventions cover Elixir only. |
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<!-- SECTION:PLAN:END -->
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## Implementation Notes
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<!-- SECTION:NOTES:BEGIN -->
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## Implementation notes
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### Step 1: Guard
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- Added `import os` after `import gc` in main.py
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- Wrapped bare `main()` call with `if os.environ.get("PRESTO_TEST_MODE") != "1":`
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- Emulator still launches: `mise run emulator` opens normally
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### Step 2: Infrastructure
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- Created `presto/tests/__init__.py`, `conftest.py`, `test_screens.py`, `fixtures/`
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- conftest sets `PRESTO_TEST_MODE=1`, provides session-scoped `_emulator` fixture
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(installs mocks + headless display), `main_module` fixture (imports main lazily),
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`init_display` fixture, and `make_mock_record()` helper
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- `fetch_thumbnail` is monkey-patched to raise RuntimeError on network access
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### Step 3: Smoke tests
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- 7 tests pass in 0.58s: home, month, day-empty, day-error, record-detail,
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search-input, search-results
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- Screenshots saved to `presto/tests/fixtures/`
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- No network calls triggered
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### Step 4: Mise task
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- Added `[tasks.test]` to `presto/mise.toml`: `pytest tests/ -v`
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- `mise run test` works from the presto directory
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### Step 5: Documentation
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- Added "Testing" section to `presto/README.md` with usage, coverage table,
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and instructions for adding new tests
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- Added "## Testing" section to `presto/AGENTS.md` with conventions
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### Key implementation difference from plan
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- Did not use `DeviceTest` as base class — instead used pytest session-scoped
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fixtures that call `install_mocks()` and `create_display()` directly. This
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allows clean pytest integration (fixtures, parametrization) without
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unittest.TestCase constraints.
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- `import main` happens lazily inside a session-scoped fixture that depends
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on the emulator setup fixture, ensuring mocks are in place before the
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module-level `Presto(full_res=True)` call executes.
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### Acceptance criteria #2 (physical deploy) remains unchecked
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Cannot verify without physical Presto device. The guard is a no-op when
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`PRESTO_TEST_MODE` is unset, so the change is semantically identical to the
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original bare `main()` call.
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<!-- SECTION:NOTES:END -->
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## Final Summary
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<!-- SECTION:FINAL_SUMMARY:BEGIN -->
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## Summary
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Added a smoke-test harness for the Presto MicroPython application using the pimoroni-emulator's mock system for headless rendering.
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### What changed
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- **`presto/main.py`** — Added `import os` and wrapped the bare `main()` call with an environment-variable guard (`if os.environ.get("PRESTO_TEST_MODE") != "1":`). The guard is a no-op in normal operation; the emulator and physical deploy paths are unchanged.
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- **`presto/tests/`** — New test directory with:
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- `conftest.py` — Session-scoped fixtures that install emulator mocks, create a headless Presto display, import `main` lazily, init pens, and monkey-patch `fetch_thumbnail` to raise on any accidental network call. Provides `make_mock_record()` helper.
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- `test_screens.py` — 7 smoke tests (home, month, day-empty, day-error, record-detail, search-input, search-results), all passing in ~0.6s.
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- `fixtures/` — 7 screenshots generated per run for manual visual inspection.
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- **`presto/mise.toml`** — Added `[tasks.test]` task: `pytest tests/ -v`.
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- **`presto/README.md`** — Added "Testing" section with usage instructions and coverage table.
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- **`presto/AGENTS.md`** — Added "## Testing" section with conventions.
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### Tests
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```
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7 passed in 0.58s
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```
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All tests use mock data with `_thumb_failed=True` / `_thumb_data=None` so no network calls occur. The `fetch_thumbnail` monkey-patch acts as a safety net.
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### Key implementation note
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Used pytest session-scoped fixtures calling `install_mocks()` + `create_display()` directly rather than extending `DeviceTest`. This avoids unittest.TestCase constraints and allows clean pytest fixture injection. `import main` happens lazily inside a fixture that depends on the emulator setup, ensuring mock modules are in `sys.modules` before the module-level `Presto(full_res=True)` call executes.
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### Outstanding
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Acceptance criterion #2 (physical Presto deployment) could not be verified without the device. The guard change is semantically a no-op when `PRESTO_TEST_MODE` is unset — the code path is identical to the original bare `main()` call.
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<!-- SECTION:FINAL_SUMMARY:END -->
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