Add helper functions for linting to testutil

Signed-off-by: beorn7 <beorn@grafana.com>

prometheus/testutil/lint.go

@@ -0,0 +1,46 @@
+// Copyright 2020 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 testutil
+
+import (
+	"fmt"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/testutil/promlint"
+)
+
+// CollectAndLint registers the provided Collector with a newly created
+// pedantic Registry. It then does the same as GatherAndLint, gathering the
+// metrics from the pedantic Registry.
+func CollectAndLint(c prometheus.Collector, metricNames ...string) ([]promlint.Problem, error) {
+	reg := prometheus.NewPedanticRegistry()
+	if err := reg.Register(c); err != nil {
+		return nil, fmt.Errorf("registering collector failed: %s", err)
+	}
+	return GatherAndLint(reg, metricNames...)
+}
+
+// GatherAndLint gathers all metrics from the provided Gatherer and checks them
+// with the linter in the promlint package. If any metricNames are provided,
+// only metrics with those names are checked.
+func GatherAndLint(g prometheus.Gatherer, metricNames ...string) ([]promlint.Problem, error) {
+	got, err := g.Gather()
+	if err != nil {
+		return nil, fmt.Errorf("gathering metrics failed: %s", err)
+	}
+	if metricNames != nil {
+		got = filterMetrics(got, metricNames)
+	}
+	return promlint.NewWithMetricFamilies(got).Lint()
+}

prometheus/testutil/lint_test.go

@@ -0,0 +1,70 @@
+// Copyright 2020 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 testutil
+
+import (
+	"testing"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+func TestCollectAndLintGood(t *testing.T) {
+	cnt := prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "some_total",
+			Help: "A value that represents a counter.",
+			ConstLabels: prometheus.Labels{
+				"label1": "value1",
+			},
+		},
+		[]string{"foo"},
+	)
+	cnt.WithLabelValues("bar")
+	cnt.WithLabelValues("baz")
+
+	problems, err := CollectAndLint(cnt)
+	if err != nil {
+		t.Error("Unexpected error:", err)
+	}
+	if len(problems) > 0 {
+		t.Error("Unexpected lint problems:", problems)
+	}
+}
+
+func TestCollectAndLintBad(t *testing.T) {
+	cnt := prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "someThing_ms",
+			Help: "A value that represents a counter.",
+			ConstLabels: prometheus.Labels{
+				"label1": "value1",
+			},
+		},
+		[]string{"fooBar"},
+	)
+	cnt.WithLabelValues("bar")
+	cnt.WithLabelValues("baz")
+
+	problems, err := CollectAndLint(cnt)
+	if err != nil {
+		t.Error("Unexpected error:", err)
+	}
+	if len(problems) < 5 {
+		// The exact nature of the lint problems found is tested within
+		// the promlint package itself. Here we only want to make sure
+		// that the collector successfully hit the linter and got enough
+		// problems flagged.
+		t.Error("Not enough lint problems found.")
+	}
+}

prometheus/testutil/testutil.go

@@ -31,6 +31,10 @@
 // testing custom prometheus.Collector implementations and in particular whole
 // exporters, i.e. programs that retrieve telemetry data from a 3rd party source
 // and convert it into Prometheus metrics.
+//
+// In a similar pattern, CollectAndLint and GatherAndLint can be used to detect
+// metrics that have issues with their name, type, or metadata without being
+// necessarily invalid, e.g. a counter with a name missing the “_total” suffix.
 package testutil
 
 import (