Covering change with unit test

This test focuses on the feature of allowing sub-routers error handlers to precede the parents, rather than the code change required to provide this functionality.

mux_test.go

@@ -1123,6 +1123,30 @@ func TestWalkNested(t *testing.T) {
 	}
 }
 
+func TestSubrouterErrorHandling(t *testing.T) {
+	superRouterCalled := false
+	subRouterCalled := false
+
+	router := NewRouter()
+	router.NotFoundHandler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		superRouterCalled = true
+	})
+	subRouter := router.PathPrefix("/bign8").Subrouter()
+	subRouter.NotFoundHandler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		subRouterCalled = true
+	})
+
+	req, _ := http.NewRequest("GET", "http://localhost/bign8/was/here", nil)
+	router.ServeHTTP(NewRecorder(), req)
+
+	if superRouterCalled {
+		t.Error("Super router 404 handler called when sub-router 404 handler is available.")
+	}
+	if !subRouterCalled {
+		t.Error("Sub-router 404 handler was not called.")
+	}
+}
+
 // ----------------------------------------------------------------------------
 // Helpers
 // ----------------------------------------------------------------------------