Trigger http client error for testing with httptest - unit-testing

Question

I have a simple function which takes a URL and fetches the response:
func getUrl(url string) (string, error) {
var theClient = &http.Client{Timeout: 12 * time.Second}
resp, err := theClient.Get(url)
if err != nil {
return "", err
}
defer r.Body.Close()
body, readErr := ioutil.ReadAll(resp.Body)
if readErr != nil {
return "", readErr
}
return string(body), nil
}
Now, I want to trigger an error on the theClient.Get(url) line but I don't know how to. I can trigger an error on the ReadAll() line, by returning no response but with content-length:2.
How can I trigger an error on the theClient.Get(url) line for my unit test?
func TestGetUrl(t *testing.T) {
server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
w.Header().Set("Content-Length", "2")
}))
defer server.Close()
gotContent, gotErr := getUrl(server.URL)
wantErr := "unexpected EOF"
if gotErr == nil || gotErr.Error() != wantErr {
t.Errorf("got err %v; wanted %s", gotErr, wantErr)
}
}

Answer 1

Easiest way is to simply pass an invalid URL:
_, err := http.Get("clearly not a valid url")
fmt.Println("Got error:", err != nil) // Got error: true
Another option is to make it timeout by sleeping in your httptest.Server handler, but that doesn't seem like a very nice idea (but you will be able to assert that it was called in the first place).