Add additional tests

This adds two tests.

The first test is to validate that two successive counter events will
increment a counter.  This is more about ensuring we can look up the
same metric twice in a row than checking increment functionality.

The second test verifies that the hashLabels function returns different
results when labels are changed.

Signed-off-by: Clayton O'Neill <claytono@github.com>

exporter_test.go

@@ -591,6 +591,51 @@ func TestHistogramUnits(t *testing.T) {
 		t.Fatalf("Received unexpected value for histogram observation %f != .300", *value)
 	}
 }
+func TestCounterIncrement(t *testing.T) {
+	// Start exporter with a synchronous channel
+	events := make(chan Events)
+	go func() {
+		testMapper := mapper.MetricMapper{}
+		testMapper.InitCache(0)
+		ex := NewExporter(&testMapper)
+		ex.Listen(events)
+	}()
+
+	// Synchronously send a statsd event to wait for handleEvent execution.
+	// Then close events channel to stop a listener.
+	name := "foo_counter"
+	labels := map[string]string{
+		"foo": "bar",
+	}
+	c := Events{
+		&CounterEvent{
+			metricName: name,
+			value:      1,
+			labels:     labels,
+		},
+		&CounterEvent{
+			metricName: name,
+			value:      1,
+			labels:     labels,
+		},
+	}
+	events <- c
+	events <- Events{}
+	close(events)
+
+	// Check histogram value
+	metrics, err := prometheus.DefaultGatherer.Gather()
+	if err != nil {
+		t.Fatalf("Cannot gather from DefaultGatherer: %v", err)
+	}
+	value := getFloat64(metrics, name, labels)
+	if value == nil {
+		t.Fatal("Counter value should not be nil")
+	}
+	if *value != 2 {
+		t.Fatalf("Counter wasn't incremented properly")
+	}
+}
 
 type statsDPacketHandler interface {
 	handlePacket(packet []byte, e chan<- Events)
@@ -764,6 +809,37 @@ mappings:
 	}
 }
 
+func TestHashLabelNames(t *testing.T) {
+	r := newRegistry(nil)
+	// Validate value hash changes and name has doesn't when just the value changes.
+	hash1, _ := r.hashLabels(map[string]string{
+		"label": "value1",
+	})
+	hash2, _ := r.hashLabels(map[string]string{
+		"label": "value2",
+	})
+	if hash1.names != hash2.names {
+		t.Fatal("Hash of label names should match, but doesn't")
+	}
+	if hash1.values == hash2.values {
+		t.Fatal("Hash of label names shouldn't match, but do")
+	}
+
+	// Validate value and name hashes change when the name changes.
+	hash1, _ = r.hashLabels(map[string]string{
+		"label1": "value",
+	})
+	hash2, _ = r.hashLabels(map[string]string{
+		"label2": "value",
+	})
+	if hash1.names == hash2.names {
+		t.Fatal("Hash of label names shouldn't match, but do")
+	}
+	if hash1.values == hash2.values {
+		t.Fatal("Hash of label names shouldn't match, but do")
+	}
+}
+
 // getFloat64 search for metric by name in array of MetricFamily and then search a value by labels.
 // Method returns a value or nil if metric is not found.
 func getFloat64(metrics []*dto.MetricFamily, name string, labels prometheus.Labels) *float64 {