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

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

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)

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

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

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)

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.

test_barkers_equation ✅ — Barker's equation unit tests + parabolic propagation