Update

vendor/tailscale.com/net/routemanager/fortest.go

@@ -0,0 +1,23 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+package routemanager
+
+import "tailscale.com/util/testenv"
+
+// forTest is an unexported type to hide the test-only methods on
+// [RouteManager] from godoc.
+type forTest struct{ rm *RouteManager }
+
+// ForTest returns a handle to test-only methods on rm. The resulting
+// type is unexported to make it very obvious in godoc that this is
+// not stable API. This method panics if called outside of tests,
+// which also centralizes all must-be-in-tests validation.
+func (rm *RouteManager) ForTest() forTest {
+	testenv.AssertInTest()
+	return forTest{rm}
+}
+
+// PeerCount returns the number of peers currently tracked. Callers
+// must serialize it with mutations like any other write-path access.
+func (f forTest) PeerCount() int { return len(f.rm.peers) }