When a client calls an API you do not control, a fake lets you test the client without depending on that external service. A fake is a limited-capability object, struct, or service that stands in for another service. section 6.6
For an API client, a local HTTP test server can simulate the external system. Define the expected API contract, then use a handler to capture the request and return test responses. This lets you check success and error handling before integration. section 6.6
A translation client
A Go test server can route requests to a handler that calls a mock translation service. Configure the mock to return a translation or an error, then assert how the client responds. section 6.6
Fakes can provide higher-fidelity interactions than simpler test doubles, but they can be complicated to write and maintain. If a fake or its surrounding tests become unwieldy, reconsider whether the design can be simplified. Because the real external API may change, monitor and log failures; more advanced patterns such as circuit breakers are outside this treatment. section 6.7 section 6.6
Listing 6.22 client_test.go
func (suite *HelloClientSuite) SetupSuite() { #1
suite.mockServerService = new(MockService)
handler := func(w http.ResponseWriter, r *http.Request) {
b, _ := ioutil.ReadAll(r.Body)
defer r.Body.Close()
var m map[string]interface{}
_ = json.Unmarshal(b, &m)
word := m["word"].(string)
language := m["language"].(string)
resp, err := suite.mockServerService.Translate(word, language) #2
if err != nil {
http.Error(w, "error", 500)
}
if resp == "" {
http.Error(w, "missing", 404)
}
w.Header().Set("Content-Type", "application/json")
_, _ = io.WriteString(w, resp)
}
mux := http.NewServeMux()
mux.HandleFunc("/", handler)
suite.server = httptest.NewServer(mux) #3
}
func (suite *HelloClientSuite) TearDownSuite() {
suite.server.Close() #4
}
See a handler that reads the request and delegates to a mock service. section 6.6
