Fix: chunkenc.MockSeriesIterator

Starts its index from 0 , but users call Next() before first sample
so it needs to start from -1

Signed-off-by: György Krajcsovits <gyorgy.krajcsovits@grafana.com>

storage/interface_test.go

@@ -0,0 +1,37 @@
+// Copyright 2024 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package storage_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/prometheus/prometheus/storage"
+	"github.com/prometheus/prometheus/tsdb/chunkenc"
+)
+
+func TestMockSeries(t *testing.T) {
+	s := storage.MockSeries([]int64{1, 2, 3}, []float64{1, 2, 3}, []string{"__name__", "foo"})
+	it := s.Iterator(nil)
+	ts := []int64{}
+	vs := []float64{}
+	for it.Next() == chunkenc.ValFloat {
+		t, v := it.At()
+		ts = append(ts, t)
+		vs = append(vs, v)
+	}
+	require.Equal(t, []int64{1, 2, 3}, ts)
+	require.Equal(t, []float64{1, 2, 3}, vs)
+}

tsdb/chunkenc/chunk.go

@@ -213,7 +213,7 @@ func MockSeriesIterator(timestamps []int64, values []float64) Iterator {
 	return &mockSeriesIterator{
 		timeStamps: timestamps,
 		values:     values,
-		currIndex:  0,
+		currIndex:  -1,
 	}
 }