Mocking http requests with Go
I used to rely on dependency injection and interfaces to mock my http clients. This worked, but was very burdensome. I learned about the httptest package which provides utilities for HTTP testing. I’ll walk through an example test I made in my weather CLI
The code which makes a network request
I ping NOAA for a weather forecast using the following code. I have a FetchForecast method which invokes fetch to perform the network request at a specific URL.
package weather
type Weather struct {
forecastUrl string
}
func (w *Weather) FetchForecast() ([]Forecast, error) {
var fr forecastReponse
err := w.fetch(w.forecastUrl, &fr)
if err != nil {
return nil, fmt.Errorf("failed to unmarshal response, %w", err)
}
return fr.Properties.Periods, nil
}
func (w *Weather) fetch(url string, unmarshal interface{}) error {
resp, err := http.Get(url)
if err != nil {
return fmt.Errorf("%w, %w", ErrFetchForecast, err)
}
defer resp.Body.Close()
if resp.StatusCode != http.StatusOK {
return fmt.Errorf("%w, got status %d", ErrFetchForecast, resp.StatusCode)
}
body, err := io.ReadAll(resp.Body)
if err != nil {
return err
}
err = json.Unmarshal(body, unmarshal)
if err != nil {
return fmt.Errorf("failed to unmarshal response, %w", err)
}
return nil
}
Writing a test for this is easy. You can use set up a mock server with httptest, and supply a URL to that server. Here is an example test where I supply a mock response from NOAA using a testing server. My code will make a GET request to this server, and receive code.
package weather_test
import (
"net/http"
"net/http/httptest"
"testing"
"github.com/Fallenstedt/weather/common/weather"
)
func TestFetchForcast(t *testing.T) {
server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
w.Write([]byte(`{
foo: "bar" // Mock JSON goes here
}`))
})) // create an http test server which responds with some JSON
defer server.Close() // close the server at the end of the test
w := weather.Weather{ForecastUrl: server.URL} // supply a server url
_, err := w.FetchForecast() // fetch data from the httptest server
if err != nil {
t.Errorf("Found error: %v", err)
}
//... add more test expectations here
}