Add three test files exercising the servertest harness:
- lifecycle_test.go: connection, disconnection, reconnection, session
replacement, and mesh formation at various sizes.
- consistency_test.go: symmetric visibility, consistent peer state,
address presence, concurrent join/leave convergence.
- weather_test.go: rapid reconnects, flapping stability, reconnect
with various delays, concurrent reconnects, and scale tests.
All tests use table-driven patterns with subtests.
Add a new hscontrol/servertest package that provides a test harness
for exercising the full Headscale control protocol in-process, using
Tailscale's controlclient.Direct as the client.
The harness consists of:
- TestServer: wraps a Headscale instance with an httptest.Server
- TestClient: wraps controlclient.Direct with NetworkMap tracking
- TestHarness: orchestrates N clients against a single server
- Assertion helpers for mesh completeness, visibility, and consistency
Export minimal accessor methods on Headscale (HTTPHandler, NoisePublicKey,
GetState, SetServerURL, StartBatcher, StartEphemeralGC) so the servertest
package can construct a working server from outside the hscontrol package.
This enables fast, deterministic tests of connection lifecycle, update
propagation, and network weather scenarios without Docker.
