diff --git a/ipn/ipnlocal/local_test.go b/ipn/ipnlocal/local_test.go
index c290fb971..d64cbb605 100644
--- a/ipn/ipnlocal/local_test.go
+++ b/ipn/ipnlocal/local_test.go
@@ -7042,3 +7042,41 @@ func toStrings[T ~string](in []T) []string {
 	}
 	return out
 }
+
+type textUpdate struct {
+	Advertise   []string
+	Unadvertise []string
+}
+
+func routeUpdateToText(u appc.RouteUpdate) textUpdate {
+	var out textUpdate
+	for _, p := range u.Advertise {
+		out.Advertise = append(out.Advertise, p.String())
+	}
+	for _, p := range u.Unadvertise {
+		out.Unadvertise = append(out.Unadvertise, p.String())
+	}
+	return out
+}
+
+func mustPrefix(ss ...string) (out []netip.Prefix) {
+	for _, s := range ss {
+		out = append(out, netip.MustParsePrefix(s))
+	}
+	return
+}
+
+// eqUpdate generates an eventbus test filter that matches an appc.RouteUpdate
+// message equal to want, or reports an error giving a human-readable diff.
+//
+// TODO(creachadair): This is copied from the appc test package, but we can't
+// put it into the appctest package because the appc tests depend on it and
+// that makes a cycle. Clean up those tests and put this somewhere common.
+func eqUpdate(want appc.RouteUpdate) func(appc.RouteUpdate) error {
+	return func(got appc.RouteUpdate) error {
+		if diff := cmp.Diff(routeUpdateToText(got), routeUpdateToText(want)); diff != "" {
+			return fmt.Errorf("wrong update (-got, +want):\n%s", diff)
+		}
+		return nil
+	}
+}