Tests for periodicMetricLister.

pkg/custom-provider/periodic_metric_lister.go

@@ -71,7 +71,9 @@ func (l *periodicMetricLister) updateMetrics() error {
 	//Cache the result.
 	l.mostRecentResult = result
 	//Let our listener know we've got new data ready for them.
-	l.callback(result)
+	if l.callback != nil {
+		l.callback(result)
+	}
 	return nil
 }
 

pkg/custom-provider/periodic_metric_lister_test.go

@@ -0,0 +1,69 @@
+package provider
+
+import (
+	"testing"
+	"time"
+
+	prom "github.com/directxman12/k8s-prometheus-adapter/pkg/client"
+	"github.com/stretchr/testify/require"
+)
+
+type fakeLister struct {
+	callCount int
+}
+
+func (f *fakeLister) ListAllMetrics() (metricUpdateResult, error) {
+	f.callCount++
+
+	return metricUpdateResult{
+		series: [][]prom.Series{
+			[]prom.Series{
+				prom.Series{
+					Name: "a_series",
+				},
+			},
+		},
+	}, nil
+}
+
+func TestWhenNewMetricsAvailableCallbackIsInvoked(t *testing.T) {
+	fakeLister := &fakeLister{}
+	targetLister, _ := NewPeriodicMetricLister(fakeLister, time.Duration(1000))
+	periodicLister := targetLister.(*periodicMetricLister)
+
+	callbackInvoked := false
+	callback := func(r metricUpdateResult) {
+		callbackInvoked = true
+	}
+
+	periodicLister.SetNotificationReceiver(callback)
+	err := periodicLister.updateMetrics()
+	require.NoError(t, err)
+	require.True(t, callbackInvoked)
+}
+
+func TestWhenListingMetricsReturnsCachedValues(t *testing.T) {
+	fakeLister := &fakeLister{}
+	targetLister, _ := NewPeriodicMetricLister(fakeLister, time.Duration(1000))
+	periodicLister := targetLister.(*periodicMetricLister)
+
+	//We haven't invoked the inner lister yet, so we should have no results.
+	resultBeforeUpdate, err := periodicLister.ListAllMetrics()
+	require.NoError(t, err)
+	require.Equal(t, 0, len(resultBeforeUpdate.series))
+	require.Equal(t, 0, fakeLister.callCount)
+
+	//We can simulate waiting for the udpate interval to pass...
+	//which should result in calling the inner lister to get the metrics.
+	err = periodicLister.updateMetrics()
+	require.NoError(t, err)
+	require.Equal(t, 1, fakeLister.callCount)
+
+	//If we list now, we should return the cached values.
+	//Make sure we got some results this time
+	//as well as that we didn't unnecessarily invoke the inner lister.
+	resultAfterUpdate, err := periodicLister.ListAllMetrics()
+	require.NoError(t, err)
+	require.NotEqual(t, 0, len(resultAfterUpdate.series))
+	require.Equal(t, 1, fakeLister.callCount)
+}