Update test for metrics server

Updates metrics server test so that it checks for the status
code and that bytes are returned.

Signed-off-by: Alex Ellis <alexellis2@gmail.com>

watchdog/metrics/metrics_test.go

@@ -1,11 +1,13 @@
 package metrics
 
 import (
+	"fmt"
+	"net/http"
 	"testing"
 	"time"
 )
 
-func Test_RegisterServer(t *testing.T) {
+func Test_Register_ProvidesBytes(t *testing.T) {
 
 	metricsPort := 31111
 
@@ -15,7 +17,41 @@ func Test_RegisterServer(t *testing.T) {
 	cancel := make(chan bool)
 	go metricsServer.Serve(cancel)
 
-	time.AfterFunc(time.Millisecond*500, func() {
+	defer func() {
 		cancel <- true
-	})
+	}()
+
+	retries := 10
+
+	for i := 0; i < retries; i++ {
+		req, _ := http.NewRequest(http.MethodGet, fmt.Sprintf("http://127.0.0.1:%d/metrics", metricsPort), nil)
+
+		res, err := http.DefaultClient.Do(req)
+
+		if err != nil {
+			t.Logf("cannot get metrics, or not ready: %s", err.Error())
+
+			time.Sleep(time.Millisecond * 100)
+			continue
+		}
+
+		wantStatus := http.StatusOK
+		if res.StatusCode != wantStatus {
+			t.Errorf("metrics gave wrong status, want: %d, got: %d", wantStatus, res.StatusCode)
+			t.Fail()
+			return
+		}
+
+		if res.Body == nil {
+			t.Errorf("metrics response should have a body")
+			t.Fail()
+			return
+		}
+		defer res.Body.Close()
+
+		return
+	}
+
+	t.Errorf("unable to get expected response from metrics server")
+	t.Fail()
 }