skip configuration updates to the most recent one (#2690)

pkg/grpc/databroker/fast_forward_test.go

@@ -0,0 +1,74 @@
+package databroker
+
+import (
+	"context"
+	"math/rand"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+type mockFF struct {
+	clear  chan struct{}
+	update chan uint64
+}
+
+func (ff *mockFF) ClearRecords(ctx context.Context) {
+	ff.clear <- struct{}{}
+}
+
+func (ff *mockFF) UpdateRecords(ctx context.Context, sv uint64, records []*Record) {
+	time.Sleep(time.Millisecond * time.Duration(rand.Intn(5)))
+	ff.update <- sv
+}
+
+func (ff *mockFF) GetDataBrokerServiceClient() DataBrokerServiceClient {
+	return nil
+}
+
+func (ff *mockFF) getUpdate(ctx context.Context) (uint64, error) {
+	select {
+	case <-ctx.Done():
+		return 0, ctx.Err()
+	case sv := <-ff.update:
+		return sv, nil
+	}
+}
+
+func TestFastForward(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second*15)
+	defer cancel()
+
+	m := &mockFF{
+		clear:  make(chan struct{}),
+		update: make(chan uint64),
+	}
+
+	f := newFastForwardHandler(ctx, m)
+
+	for x := 0; x < 100; x++ {
+		n := rand.Intn(100) + 1
+		for i := 1; i <= n; i++ {
+			f.UpdateRecords(ctx, uint64(i), nil)
+		}
+
+		var prev uint64
+		assert.Eventually(t, func() bool {
+			sv, err := m.getUpdate(ctx)
+			require.NoError(t, err)
+			assert.Less(t, prev, sv)
+			prev = sv
+			t.Log(x, sv)
+			return int(sv) == n
+		}, time.Second, time.Millisecond*10)
+
+		f.ClearRecords(ctx)
+		select {
+		case <-ctx.Done():
+			t.Error("timed out")
+		case <-m.clear:
+		}
+	}
+}