Alerting: Fix screenshots were not cached (#58493)

pkg/services/ngalert/image/cache_test.go

@@ -0,0 +1,38 @@
+package image
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/grafana/grafana/pkg/services/ngalert/models"
+)
+
+func TestInmemCacheService(t *testing.T) {
+	s := NewInmemCacheService(time.Second, prometheus.DefaultRegisterer)
+	ctx := context.Background()
+
+	// should be a miss
+	actual, ok := s.Get(ctx, "test")
+	assert.False(t, ok)
+	assert.Equal(t, models.Image{}, actual)
+
+	// should be a hit
+	expected := models.Image{Path: "test.png"}
+	require.NoError(t, s.Set(ctx, "test", expected))
+	actual, ok = s.Get(ctx, "test")
+	assert.True(t, ok)
+	assert.Equal(t, expected, actual)
+
+	// wait 1s and the cached image should have expired
+	<-time.After(time.Second)
+
+	// should be a miss
+	actual, ok = s.Get(ctx, "test")
+	assert.False(t, ok)
+	assert.Equal(t, models.Image{}, actual)
+}