From a693dd19f244f000da40bcbac85041846b78cfc1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Gy=C3=B6rgy=20Krajcsovits?= <gyorgy.krajcsovits@grafana.com>
Date: Fri, 30 Aug 2024 16:44:36 +0200
Subject: [PATCH] Fix: chunkenc.MockSeriesIterator
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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 | 37 +++++++++++++++++++++++++++++++++++++
 tsdb/chunkenc/chunk.go    |  2 +-
 2 files changed, 38 insertions(+), 1 deletion(-)
 create mode 100644 storage/interface_test.go

diff --git a/storage/interface_test.go b/storage/interface_test.go
new file mode 100644
index 000000000..ba6072173
--- /dev/null
+++ b/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)
+}
diff --git a/tsdb/chunkenc/chunk.go b/tsdb/chunkenc/chunk.go
index 1421f3b39..7082f34c3 100644
--- a/tsdb/chunkenc/chunk.go
+++ b/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,
 	}
 }