feat(coderd): add prometheus metrics to servertailnet (#11988)

testutil/prometheus.go

@@ -0,0 +1,50 @@
+package testutil
+
+import (
+	"testing"
+
+	dto "github.com/prometheus/client_model/go"
+	"github.com/stretchr/testify/require"
+)
+
+func PromGaugeHasValue(t testing.TB, metrics []*dto.MetricFamily, value float64, name string, label ...string) bool {
+	t.Helper()
+	for _, family := range metrics {
+		if family.GetName() != name {
+			continue
+		}
+		ms := family.GetMetric()
+	metricsLoop:
+		for _, m := range ms {
+			require.Equal(t, len(label), len(m.GetLabel()))
+			for i, lv := range label {
+				if lv != m.GetLabel()[i].GetValue() {
+					continue metricsLoop
+				}
+			}
+			return value == m.GetGauge().GetValue()
+		}
+	}
+	return false
+}
+
+func PromCounterHasValue(t testing.TB, metrics []*dto.MetricFamily, value float64, name string, label ...string) bool {
+	t.Helper()
+	for _, family := range metrics {
+		if family.GetName() != name {
+			continue
+		}
+		ms := family.GetMetric()
+	metricsLoop:
+		for _, m := range ms {
+			require.Equal(t, len(label), len(m.GetLabel()))
+			for i, lv := range label {
+				if lv != m.GetLabel()[i].GetValue() {
+					continue metricsLoop
+				}
+			}
+			return value == m.GetCounter().GetValue()
+		}
+	}
+	return false
+}