add unit test for annotations

Signed-off-by: Jeanette Tan <jeanette.tan@grafana.com>

util/annotations/annotations_test.go

@@ -0,0 +1,45 @@
+// 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 annotations
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/prometheus/prometheus/promql/parser/posrange"
+)
+
+func TestAnnotations_AsStrings(t *testing.T) {
+	var annos Annotations
+	pos := posrange.PositionRange{Start: 3, End: 8}
+
+	annos.Add(errors.New("this is a non-annotation error"))
+
+	annos.Add(NewInvalidRatioWarning(1.1, 100, pos))
+	annos.Add(NewInvalidRatioWarning(1.2, 123, pos))
+
+	annos.Add(NewHistogramIgnoredInAggregationInfo("sum", pos))
+
+	warnings, infos := annos.AsStrings("lorem ipsum dolor sit amet", 0, 0)
+	require.ElementsMatch(t, warnings, []string{
+		"this is a non-annotation error",
+		"PromQL warning: ratio value should be between -1 and 1, got 1.1, capping to 100 (1:4)",
+		"PromQL warning: ratio value should be between -1 and 1, got 1.2, capping to 123 (1:4)",
+	})
+	require.ElementsMatch(t, infos, []string{
+		"PromQL info: ignored histogram in sum aggregation (1:4)",
+	})
+}