test: cut low-value tests, rewrite the rest around behavior, parallelize lanes (#285)

docs/workflow/testing.md

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+<!-- read_when: writing, reviewing, or deleting tests -->
+
+# Testing Guidelines
+
+Status: active  
+Last verified: 2026-10-04  
+Owner: Kyle Yasuda  
+Read when: adding or changing tests
+
+Which lanes to run lives in [Verification](./verification.md). This page covers what a
+good test looks like here.
+
+## Test Behavior, Not Wiring
+
+- Exercise a module through its public interface and assert outcomes: return values,
+  resulting state, files written, rows in sqlite, messages sent to a fake process.
+- Prefer real collaborators that are cheap: tmp dirs, in-memory or tmp sqlite, fake
+  executables, pure parsers. Fake only the edges (Electron, mpv socket, network).
+- Assert call order only when order is the behavior (startup sequencing, ABA races),
+  and then assert relative order, not the whole call log.
+
+## Do Not Write
+
+- Pass-through tests: a builder or handler that only forwards deps (`*-main-deps.ts`,
+  `*-runtime-handlers.ts`) needs no test. TypeScript already checks the shape.
+- Source-text tests: reading `.ts`, `.css`, `.html`, `.lua`, `.swift`, or workflow YAML
+  and asserting with regexes. If the invariant matters, extract the logic and run it
+  (see `src/preload-ipc-listeners.ts`). Policy lints over workflow YAML are the
+  exception and belong in one parsed-YAML check.
+- "Stays deleted" tests for removed modules, flags, or selectors. `tsc` and review
+  catch reintroduction.
+- Tests that restate constants, defaults, labels, or window options.
+- The same rule at several layers. Test a rule once where it lives; keep one
+  end-to-end case (for the tokenizer, the golden corpus) for integration.
+
+## Keep Tests Small
+
+- Shared setup goes in a `makeDeps(overrides)` helper or a `*-test-harness.ts` file, not
+  pasted into every test.
+- Near-identical cases become a table: `for (const c of cases) test(c.name, ...)`.
+- Inject timers, clocks, and loggers instead of patching globals or private members.
+- A bug fix gets a regression test for the behavior that broke, named after the
+  behavior, not the ticket.
+
+## Known Debt
+
+- `src/main/main-wiring.test.ts` and `src/renderer/renderer-init-order.test.ts` still
+  regex `main.ts` / `renderer.ts` to guard startup ordering. Replace each test with a
+  behavioral one as the logic moves out of `main.ts` closures.