appc: log how often routeInfo is stored

So that we have some debugging info if users have trouble with storing
the routeInfo.

Updates #11008

Signed-off-by: Fran Bull <fran@tailscale.com>

appc/appconnector_test.go

@@ -9,10 +9,12 @@ import (
 	"reflect"
 	"slices"
 	"testing"
+	"time"
 
 	xmaps "golang.org/x/exp/maps"
 	"golang.org/x/net/dns/dnsmessage"
 	"tailscale.com/appc/appctest"
+	"tailscale.com/tstest"
 	"tailscale.com/util/mak"
 	"tailscale.com/util/must"
 )
@@ -520,3 +522,50 @@ func TestRoutesWithout(t *testing.T) {
 	assert("a has fewer", routesWithout(prefixes("1.1.1.1/32", "1.1.1.2/32"), prefixes("1.1.1.1/32", "1.1.1.2/32", "1.1.1.3/32", "1.1.1.4/32")), []netip.Prefix{})
 	assert("a has more", routesWithout(prefixes("1.1.1.1/32", "1.1.1.2/32", "1.1.1.3/32", "1.1.1.4/32"), prefixes("1.1.1.1/32", "1.1.1.3/32")), prefixes("1.1.1.2/32", "1.1.1.4/32"))
 }
+
+func TestRateLogger(t *testing.T) {
+	clock := tstest.Clock{}
+	wasCalled := false
+	rl := newRateLogger(func() time.Time { return clock.Now() }, 1*time.Second, func(count int64, _ time.Time) {
+		if count != 3 {
+			t.Fatalf("count for prev period: got %d, want 3", count)
+		}
+		wasCalled = true
+	})
+
+	for i := 0; i < 3; i++ {
+		clock.Advance(1 * time.Millisecond)
+		rl.update()
+		if wasCalled {
+			t.Fatalf("wasCalled: got true, want false")
+		}
+	}
+
+	clock.Advance(1 * time.Second)
+	rl.update()
+	if !wasCalled {
+		t.Fatalf("wasCalled: got false, want true")
+	}
+
+	wasCalled = false
+	rl = newRateLogger(func() time.Time { return clock.Now() }, 1*time.Hour, func(count int64, _ time.Time) {
+		if count != 3 {
+			t.Fatalf("count for prev period: got %d, want 3", count)
+		}
+		wasCalled = true
+	})
+
+	for i := 0; i < 3; i++ {
+		clock.Advance(1 * time.Minute)
+		rl.update()
+		if wasCalled {
+			t.Fatalf("wasCalled: got true, want false")
+		}
+	}
+
+	clock.Advance(1 * time.Hour)
+	rl.update()
+	if !wasCalled {
+		t.Fatalf("wasCalled: got false, want true")
+	}
+}