metrics/prometheus: define TYPE once, add tests (#21068)

* metrics/prometheus: define type once for histograms

* metrics/prometheus: test collector

metrics/prometheus/collector_test.go

@@ -0,0 +1,110 @@
+package prometheus
+
+import (
+	"os"
+	"testing"
+	"time"
+
+	"github.com/ethereum/go-ethereum/metrics"
+)
+
+func TestMain(m *testing.M) {
+	metrics.Enabled = true
+	os.Exit(m.Run())
+}
+
+func TestCollector(t *testing.T) {
+	c := newCollector()
+
+	counter := metrics.NewCounter()
+	counter.Inc(12345)
+	c.addCounter("test/counter", counter)
+
+	gauge := metrics.NewGauge()
+	gauge.Update(23456)
+	c.addGauge("test/gauge", gauge)
+
+	gaugeFloat64 := metrics.NewGaugeFloat64()
+	gaugeFloat64.Update(34567.89)
+	c.addGaugeFloat64("test/gauge_float64", gaugeFloat64)
+
+	histogram := metrics.NewHistogram(&metrics.NilSample{})
+	c.addHistogram("test/histogram", histogram)
+
+	meter := metrics.NewMeter()
+	defer meter.Stop()
+	meter.Mark(9999999)
+	c.addMeter("test/meter", meter)
+
+	timer := metrics.NewTimer()
+	defer timer.Stop()
+	timer.Update(20 * time.Millisecond)
+	timer.Update(21 * time.Millisecond)
+	timer.Update(22 * time.Millisecond)
+	timer.Update(120 * time.Millisecond)
+	timer.Update(23 * time.Millisecond)
+	timer.Update(24 * time.Millisecond)
+	c.addTimer("test/timer", timer)
+
+	resettingTimer := metrics.NewResettingTimer()
+	resettingTimer.Update(10 * time.Millisecond)
+	resettingTimer.Update(11 * time.Millisecond)
+	resettingTimer.Update(12 * time.Millisecond)
+	resettingTimer.Update(120 * time.Millisecond)
+	resettingTimer.Update(13 * time.Millisecond)
+	resettingTimer.Update(14 * time.Millisecond)
+	c.addResettingTimer("test/resetting_timer", resettingTimer.Snapshot())
+
+	emptyResettingTimer := metrics.NewResettingTimer().Snapshot()
+	c.addResettingTimer("test/empty_resetting_timer", emptyResettingTimer)
+
+	const expectedOutput = `# TYPE test_counter gauge
+test_counter 12345
+
+# TYPE test_gauge gauge
+test_gauge 23456
+
+# TYPE test_gauge_float64 gauge
+test_gauge_float64 34567.89
+
+# TYPE test_histogram_count counter
+test_histogram_count 0
+
+# TYPE test_histogram summary
+test_histogram {quantile="0.5"} 0
+test_histogram {quantile="0.75"} 0
+test_histogram {quantile="0.95"} 0
+test_histogram {quantile="0.99"} 0
+test_histogram {quantile="0.999"} 0
+test_histogram {quantile="0.9999"} 0
+
+# TYPE test_meter gauge
+test_meter 9999999
+
+# TYPE test_timer_count counter
+test_timer_count 6
+
+# TYPE test_timer summary
+test_timer {quantile="0.5"} 2.25e+07
+test_timer {quantile="0.75"} 4.8e+07
+test_timer {quantile="0.95"} 1.2e+08
+test_timer {quantile="0.99"} 1.2e+08
+test_timer {quantile="0.999"} 1.2e+08
+test_timer {quantile="0.9999"} 1.2e+08
+
+# TYPE test_resetting_timer_count counter
+test_resetting_timer_count 6
+
+# TYPE test_resetting_timer summary
+test_resetting_timer {quantile="0.50"} 12000000
+test_resetting_timer {quantile="0.95"} 120000000
+test_resetting_timer {quantile="0.99"} 120000000
+
+`
+	exp := c.buff.String()
+	if exp != expectedOutput {
+		t.Log("Expected Output:\n", expectedOutput)
+		t.Log("Actual Output:\n", exp)
+		t.Fatal("unexpected collector output")
+	}
+}