Merge pull request #499 from PhilipGough/fixes-498

Fixes 498

prometheus/testutil/testutil.go

@@ -138,20 +138,13 @@ func GatherAndCompare(g prometheus.Gatherer, expected io.Reader, metricNames ...
 	}
 	want := internal.NormalizeMetricFamilies(wantRaw)
 
-	if len(got) != len(want) {
+	return compare(got, want)
-		return notMatchingError(got, want)
-	}
-	for i := range got {
-		if got[i].String() != want[i].String() {
-			return notMatchingError(got, want)
-		}
-	}
-	return nil
 }
 
-// notMatchingError encodes both provided slices of metric families into the
+// compare encodes both provided slices of metric families into the text format,
-// text format and creates a readable error message from the result.
+// compares their string message, and returns an error if they do not match.
-func notMatchingError(got, want []*dto.MetricFamily) error {
+// The error contains the encoded text, of both the desired, and actual result.
+func compare(got, want []*dto.MetricFamily) error {
 	var gotBuf, wantBuf bytes.Buffer
 	enc := expfmt.NewEncoder(&gotBuf, expfmt.FmtText)
 	for _, mf := range got {
@@ -166,6 +159,7 @@ func notMatchingError(got, want []*dto.MetricFamily) error {
 		}
 	}
 
+	if wantBuf.String() != gotBuf.String() {
 		return fmt.Errorf(`
 metric output does not match expectation; want:
 
@@ -175,6 +169,9 @@ got:
 
 %s
 `, wantBuf.String(), gotBuf.String())
+
+	}
+	return nil
 }
 
 func filterMetrics(metrics []*dto.MetricFamily, names []string) []*dto.MetricFamily {

prometheus/testutil/testutil_test.go

@@ -165,6 +165,82 @@ func TestCollectAndCompareNoLabel(t *testing.T) {
 	}
 }
 
+func TestCollectAndCompareHistogram(t *testing.T) {
+	inputs := []struct {
+		name        string
+		c           prometheus.Collector
+		metadata    string
+		expect      string
+		labels      []string
+		observation float64
+	}{
+		{
+			name: "Testing Histogram Collector",
+			c: prometheus.NewHistogram(prometheus.HistogramOpts{
+				Name:    "some_histogram",
+				Help:    "An example of a histogram",
+				Buckets: []float64{1, 2, 3},
+			}),
+			metadata: `
+				# HELP some_histogram An example of a histogram
+				# TYPE some_histogram histogram
+			`,
+			expect: `
+				some_histogram{le="1"} 0
+				some_histogram{le="2"} 0
+				some_histogram{le="3"} 1
+        			some_histogram_bucket{le="+Inf"} 1
+        			some_histogram_sum 2.5
+        			some_histogram_count 1
+
+			`,
+			observation: 2.5,
+		},
+		{
+			name: "Testing HistogramVec Collector",
+			c: prometheus.NewHistogramVec(prometheus.HistogramOpts{
+				Name:    "some_histogram",
+				Help:    "An example of a histogram",
+				Buckets: []float64{1, 2, 3},
+			}, []string{"test"}),
+
+			metadata: `
+				# HELP some_histogram An example of a histogram
+				# TYPE some_histogram histogram
+			`,
+			expect: `
+            			some_histogram_bucket{test="test",le="1"} 0
+            			some_histogram_bucket{test="test",le="2"} 0
+            			some_histogram_bucket{test="test",le="3"} 1
+            			some_histogram_bucket{test="test",le="+Inf"} 1
+            			some_histogram_sum{test="test"} 2.5
+           		 	some_histogram_count{test="test"} 1
+		
+			`,
+			observation: 2.5,
+		},
+	}
+
+	for _, input := range inputs {
+		switch collector := input.c.(type) {
+		case prometheus.Histogram:
+			collector.Observe(input.observation)
+		case *prometheus.HistogramVec:
+			collector.WithLabelValues("test").Observe(input.observation)
+		default:
+			t.Fatalf("unsuported collector tested")
+
+		}
+
+		t.Run(input.name, func(t *testing.T) {
+			if err := CollectAndCompare(input.c, strings.NewReader(input.metadata+input.expect)); err != nil {
+				t.Errorf("unexpected collecting result:\n%s", err)
+			}
+		})
+
+	}
+}
+
 func TestNoMetricFilter(t *testing.T) {
 	const metadata = `
 		# HELP some_total A value that represents a counter.