Add test to expose #580

Tests are heavily inspired by @shturec, see #584.

Signed-off-by: beorn7 <bjoern@rabenste.in>

prometheus/promhttp/instrument_client_test.go

@@ -14,15 +14,18 @@
 package promhttp
 
 import (
+	"context"
+	"fmt"
 	"log"
 	"net/http"
+	"net/http/httptest"
 	"testing"
 	"time"
 
 	"github.com/prometheus/client_golang/prometheus"
 )
 
-func TestClientMiddlewareAPI(t *testing.T) {
+func makeInstrumentedClient() (*http.Client, *prometheus.Registry) {
 	client := http.DefaultClient
 	client.Timeout = 1 * time.Second
 
@@ -92,12 +95,100 @@ func TestClientMiddlewareAPI(t *testing.T) {
 			),
 		),
 	)
+	return client, reg
+}
 
-	resp, err := client.Get("http://google.com")
+func TestClientMiddlewareAPI(t *testing.T) {
+	client, reg := makeInstrumentedClient()
+	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer backend.Close()
+
+	resp, err := client.Get(backend.URL)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+
+	mfs, err := reg.Gather()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if want, got := 3, len(mfs); want != got {
+		t.Fatalf("unexpected number of metric families gathered, want %d, got %d", want, got)
+	}
+	for _, mf := range mfs {
+		if len(mf.Metric) == 0 {
+			t.Errorf("metric family %s must not be empty", mf.GetName())
+		}
+	}
+}
+
+func TestClientMiddlewareAPIWithRequestContext(t *testing.T) {
+	client, reg := makeInstrumentedClient()
+	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer backend.Close()
+
+	req, err := http.NewRequest("GET", backend.URL, nil)
 	if err != nil {
 		t.Fatalf("%v", err)
 	}
+
+	// Set a context with a long timeout.
+	ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
+	defer cancel()
+	req = req.WithContext(ctx)
+
+	resp, err := client.Do(req)
+	if err != nil {
+		t.Fatal(err)
+	}
 	defer resp.Body.Close()
+
+	mfs, err := reg.Gather()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if want, got := 3, len(mfs); want != got {
+		t.Fatalf("unexpected number of metric families gathered, want %d, got %d", want, got)
+	}
+	for _, mf := range mfs {
+		if len(mf.Metric) == 0 {
+			t.Errorf("metric family %s must not be empty", mf.GetName())
+		}
+	}
+}
+
+func TestClientMiddlewareAPIWithRequestContextTimeout(t *testing.T) {
+	client, _ := makeInstrumentedClient()
+
+	// Slow testserver responding in 100ms.
+	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		time.Sleep(100 * time.Millisecond)
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer backend.Close()
+
+	req, err := http.NewRequest("GET", backend.URL, nil)
+	if err != nil {
+		t.Fatalf("%v", err)
+	}
+
+	// Set a context with a short timeout.
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Millisecond)
+	defer cancel()
+	req = req.WithContext(ctx)
+
+	_, err = client.Do(req)
+	if err == nil {
+		t.Fatal("did not get timeout error")
+	}
+	if want, got := fmt.Sprintf("Get %s: context deadline exceeded", backend.URL), err.Error(); want != got {
+		t.Fatalf("want error %q, got %q", want, got)
+	}
 }
 
 func ExampleInstrumentRoundTripperDuration() {