flow/manager: Make TestDialCachedConn actually test something.

Change-Id: I7bd33f33deb95d0ae50dbd980103930aa9878cd5
diff --git a/runtime/internal/flow/manager/manager_test.go b/runtime/internal/flow/manager/manager_test.go
index 1b92c1b..9752a56 100644
--- a/runtime/internal/flow/manager/manager_test.go
+++ b/runtime/internal/flow/manager/manager_test.go
@@ -64,11 +64,15 @@
 	if got, want := len(dm.(*manager).cache.addrCache), 1; got != want {
 		t.Fatalf("got cache size %v, want %v", got, want)
 	}
+	old := dm.(*manager).cache.ridCache[am.RoutingID()]
 	// After dialing another connection the cache should still hold one connection
 	// because the connections should be reused.
 	testFlows(t, ctx, dm, am, flowtest.BlessingsForPeer)
 	if got, want := len(dm.(*manager).cache.addrCache), 1; got != want {
-		t.Fatalf("got cache size %v, want %v", got, want)
+		t.Errorf("got cache size %v, want %v", got, want)
+	}
+	if c := dm.(*manager).cache.ridCache[am.RoutingID()]; c != old {
+		t.Errorf("got %v want %v", c, old)
 	}
 
 	shutdown()