Testing strategy

evolving

Testing strategy

TL;DR. Three layers: unit tests beside code, proptest for codec roundtrips and state-machine invariants and replay equivalence, insta snapshot tests for wire bytes and rendered TUI frames. Mutation testing with cargo-mutants once the codebase is big enough to warrant it; target is 90% on protocol and core.

Three layers:

  1. Unit tests colocated with code. Standard.
  2. Property tests (proptest) for:
    • Protocol codec roundtrip (encode → decode → equal).
    • State machine invariants (e.g. “after any sequence of Commands, the layout tree is well-formed”).
    • Replay equivalence: for any PTY byte stream bs, writing bs to a fresh Terminal on the client reproduces the same visible grid as the server’s Terminal saw, up to the documented downsampling rewrites. The snapshot-on-attach synthesis algorithm (research/2026-05-25-libghostty-renderstate.md §7) is checked the same way: synthesize, replay into a fresh Terminal, compare RenderState snapshots.
  3. Snapshot tests (insta) for:
    • Wire bytes of representative messages, so accidental format changes are loud.
    • Rendered TUI frames (a CellGrid → ASCII art helper).

We will adopt cargo-mutants once the codebase is substantial. The bar: mutation score above 90% on the protocol and core crates.