- One `SCENARIO("description")` per logical test group, with `[tag1][tag2]` annotations
- Run `./build/orbit_test --list-tags` to see tags used by other tests. Original tags from the old test file are a useful starting point, but the implementor has discretion to choose appropriate tags.
- **Use SCENARIO to share setup/teardown across multiple SECTIONs.** Catch2 re-initializes the fixture before each SECTION, so declare shared constants, structs, and variables in the SCENARIO body (between the opening `{` and the first `SECTION`). These persist across all SECTIONs within the SCENARIO.
- Example: a `SimulationState* sim` created once in the SCENARIO body, then each SECTION mutates and tests it independently.
- **Use SCENARIO as a shared fixture** for setup/initialization. SECTIONs represent **different test scenarios** that branch from that fixture with distinct operations. Avoid using SECTIONs as section headers to group assertions about the same result — group related assertions into fewer SECTIONs instead.
- Catch2 re-initializes the fixture before each SECTION, so shared constants, structs, and variables declared in the SCENARIO body run fresh per SECTION. This is intentional: each SECTION should test a different code path or mutation of the fixture.
- Example: one SECTION checks the initial state before modification; a separate SECTION applies a burn and checks all post-burn results.
- Embed expected values directly in `WithinAbs()` calls (see Section 4 for precalc script usage). No need to declare named constants unless the value is reused.
- **No decorative comments.** Do not add `// (Old: ...)` comments, `===` separators, `---` separators, or any other decorative annotations. The SECTION description string is the documentation.
- **Use `REQUIRE()` for integer comparisons**, `WithinAbs()` only for floating-point. E.g., `REQUIRE(sim->body_count == 2)` not `REQUIRE_THAT(sim->body_count, WithinAbs(2.0, 0.001))`.
