# Test Refactoring Optimization Strategy

## Tooling
- `scripts/sim_engine.py` — Generic orbital mechanics simulator (Python, TOML 1.0 configs)
  - Replicates C++ physics: Kepler propagation, orbital↔Cartesian transforms, drift detection
  - Multi-body hierarchical propagation with global/local coordinate tracking
  - Use for precalculating expected values (transition times, final states, energy conservation)
- TOML configs in `tests/` must use TOML 1.0 inline table syntax (single-line `{}`)
  - Old configs in `old_tests/` use multiline inline tables (toml-c17 style) — keep for reference
  - Python's `tomllib` requires single-line inline tables

## Sim Engine Capabilities
### Implemented
- Body propagation (elliptical + parabolic via Barker's equation)
- Orbital↔Cartesian transforms (full z-x-z Euler rotation)
- Velocity drift detection and element reconstruction
- Global coordinate computation (hierarchical parent→child)
- Spacecraft struct, loading, propagation
- Impulsive burns (prograde, retrograde, normal, antinormal, radial_in, radial_out, custom)
- TOML 1.0 config parsing
### NOT Implemented (notify the user before beginning to refactor)
- SOI transitions
- Maneuver trigger system (TRIGGER_TIME, TRIGGER_TRUE_ANOMALY)
- Hohmann transfer calculations
- Rendezvous planning
- OrbitTracker
- Energy functions (KE, PE, total)
- Hyperbolic propagation

## 1. Structure
- One `SCENARIO("description")` per logical test group, with `[tag1][tag2]` annotations
- Shared fixture: all constants, structs, and variables declared between `SCENARIO` opening and first `SECTION`
- Precompute expected values analytically at fixture level (use `scripts/*.py` for complex simulations)

## 2. Duplication elimination
- Use lambdas that capture the fixture for repeated setup→call→assert patterns
- Reuse shared structs in-place (mutate fields rather than recreating)
- Single-line `SECTION`s when body is one statement: `SECTION("name") { helper(arg); }`

## 3. Assertions
- `using Catch::Matchers::WithinAbs;` after includes
- `REQUIRE_THAT(value, WithinAbs(expected, tolerance))` — never `Approx()`
- Tolerances based on actual observed errors, tightened aggressively (1e-12 for angles, 1e-6 for meters, etc.)
- Replace qualitative checks (`a > b`) with quantitative (`WithinAbs(expected, tol)`)
- `INFO("label: " << value)` for debugging context

## 4. Precalc scripts
- For each test file, create `scripts/precalc_<test_name>.py` that computes expected values.
- **Check the capability matrix first** — only use sim_engine.py for implemented features.
- **Always output local-frame values** (distances from parent, not global from origin).
  - C++ tests typically use local coordinates (e.g., `vec3_distance(craft->local_position, (Vec3){0,0,0})`).
  - Global distances are dominated by parent body positions (e.g., Earth-Sun distance swamps LEO orbit).
- Output C++-style comments with precalculated constants for embedding in the test.
- Run with: `python3 scripts/precalc_<test_name>.py`
- If sim_engine.py lacks a feature, use analytical formulas instead (**but notify the user what feature was missing**)

## 5. Process per file
- **Pre-check**: Verify the test file has a TOML config in `old_tests/`. If it doesn't, skip — it's likely hardcoded.
- **Pre-check**: Check if the test is already in `tests/` (already refactored). Skip if so.
- **Pre-check**: Check the capability matrix — if the test needs SOI, maneuvers, rendezvous, etc., flag this before starting.
- Process **one test file at a time**.
- Create `scripts/precalc_<test_name>.py` and run it to get expected values.
- Copy from `old_tests/` to `tests/`, rewrite using the pattern from `test_true_anomaly_roundtrip.cpp`.
- Rewrite TOML configs to TOML 1.0 inline table syntax (single-line `{}`).
- Build and verify: `make test-build` then `./build/orbit_test '[tag]' -s`.
- Run full suite: `make test`.
- **Verify no other tests broke** — the new test shouldn't affect unrelated tests.
- Note any sim_engine.py features that were missing for this test (add to capability matrix if needed).
- notify the user about any broken tests (e.g., OrbitTracker bugs)
- **Always ask for review** before moving to the next file.
- **Only commit when asked.**