add metrics package test

pkg/metrics/metrics_test.go

+// Copyright 2020 The Swarm Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package metrics_test
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/ethersphere/bee/pkg/metrics"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+func TestPrometheusCollectorsFromFields(t *testing.T) {
+	s := newService()
+	collectors := metrics.PrometheusCollectorsFromFields(s)
+
+	if l := len(collectors); l != 2 {
+		t.Fatalf("got %v collectors %+v, want 2", l, collectors)
+	}
+
+	m1 := collectors[0].(prometheus.Metric).Desc().String()
+	if !strings.Contains(m1, "api_request_count") {
+		t.Errorf("unexpected metric %s", m1)
+	}
+
+	m2 := collectors[1].(prometheus.Metric).Desc().String()
+	if !strings.Contains(m2, "api_response_duration_seconds") {
+		t.Errorf("unexpected metric %s", m2)
+	}
+}
+
+type service struct {
+	// valid metrics
+	RequestCount     prometheus.Counter
+	ResponseDuration prometheus.Histogram
+	// invalid metrics
+	unexportedCount    prometheus.Counter
+	UninitializedCount prometheus.Counter
+}
+
+func newService() *service {
+	return &service{
+		RequestCount: prometheus.NewCounter(prometheus.CounterOpts{
+			Name: "api_request_count",
+			Help: "Number of API requests.",
+		}),
+		ResponseDuration: prometheus.NewHistogram(prometheus.HistogramOpts{
+			Name:    "api_response_duration_seconds",
+			Help:    "Histogram of API response durations.",
+			Buckets: []float64{0.01, 0.1, 0.25, 0.5, 1, 2.5, 5, 10},
+		}),
+		unexportedCount: prometheus.NewCounter(prometheus.CounterOpts{
+			Name: "api_unexported_count",
+			Help: "This metrics should not be discoverable by metrics.PrometheusCollectorsFromFields.",
+		}),
+	}
+}