Rewrite docs/Testing.md as a focused testing guide

AGENTS.md

@@ -174,30 +174,7 @@ Exceptions:
 - `interactive-sigint.test.ts` — needs a longer duration for SIGINT testing
 - Help output checks — testing that `--help` mentions `--duration` is fine
 
-**Test structure:**
-- `test/unit/` — Fast, mocked tests. Auth via `MockConfigManager` (automatic). Only set `ABLY_API_KEY` env var when testing env var override behavior.
-- `test/integration/` — Integration tests (e.g., interactive mode). Mocked external services but tests multi-component interaction.
-- `test/tty/` — Interactive mode tests requiring a real pseudo-TTY (e.g., SIGINT/Ctrl+C with readline). Uses `node-pty`. Local only — cannot run in CI.
-- `test/e2e/` — Full scenarios against real Ably. Auth via env vars (`ABLY_API_KEY`, `ABLY_ACCESS_TOKEN`).
-- Helpers in `test/helpers/` — `runCommand()`, `runLongRunningBackgroundProcess()`, `e2e-test-helper.ts`, `mock-config-manager.ts`.
-
-**Required test describe blocks** (exact names — every unit test file must have all 5):
-1. `"help"` — verify `--help` shows USAGE
-2. `"argument validation"` — test required args or unknown flag rejection
-3. `"functionality"` — core happy-path behavior
-4. `"flags"` — verify flags exist and work
-5. `"error handling"` — API errors, network failures
-
-Do NOT use variants like `"command arguments and flags"`, `"command flags"`, `"flag options"`, or `"parameter validation"`. Exempt: `interactive.test.ts`, `interactive-sigint.test.ts`, `bench/*.test.ts`.
-
-**Running tests:**
-```bash
-pnpm test:unit                    # All unit tests
-pnpm test:integration             # Integration tests
-pnpm test:tty                     # TTY tests (local only, needs real terminal)
-pnpm test:e2e                     # All E2E tests
-pnpm test test/unit/commands/foo.test.ts  # Specific test
-```
+See [`docs/Testing.md`](../docs/Testing.md) for test layers, directory layout, required describe blocks, running tests, helpers reference, and conventions.
 
 ## CLI Output & Flag Conventions