Change:
<ins> /* Copyright 2021 The Kubernetes 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 metrics import ( "fmt" "math/rand" "testing" "time" "k8s.io/apimachinery/pkg/util/clock" compbasemetrics "k8s.io/component-base/metrics" "k8s.io/component-base/metrics/legacyregistry" "k8s.io/klog/v2" ) const ( samplesHistName       = "sawtestsamples" samplingPeriod        = time.Millisecond ddtRangeCentiPeriods  = 300 ddtOffsetCentiPeriods = 50 numIterations         = 100 ) /* TestSampler does a rough behavioral test of the sampling in a SampleAndWatermarkHistograms.  The test creates one and exercises it, checking that the count in the sampling histogram is correct at each step.  The sampling histogram is expected to get one observation at the end of each sampling period.  A fake clock is used, and the exercise consists of repeatedly changing that fake clock by an amount of time chosen uniformly at random from a range that goes from a little negative to somewhat more than two sampling periods.  The negative changes are included because small negative changes have been observed in real monotonic clock readings (see issue #96459) and we want to test that they are properly tolerated. The designed toleration is to pretend that the clock did not change, until it resumes net forward progress. */ func TestSampler(t *testing.T) { t0 := time.Now() clk := clock.NewFakePassiveClock(t0) buckets := []float64{0, 1} gen := NewSampleAndWaterMarkHistogramsGenerator(clk, samplingPeriod, &compbasemetrics.HistogramOpts{Name: samplesHistName, Buckets: buckets}, &compbasemetrics.HistogramOpts{Name: "marks", Buckets: buckets}, []string{}) saw := gen.Generate(0, 1, []string{}) regs := gen.metrics() for _, reg := range regs { legacyregistry.MustRegister(reg) } // `dt` is the admitted cumulative difference in fake time // since the start of the test.  "admitted" means this is // never allowed to decrease, which matches the designed // toleration for negative monotonic clock changes. var dt time.Duration // `t1` is the current fake time t1 := t0.Add(dt) klog.Infof("Expect about %v warnings about time going backwards; this is fake time deliberately misbehaving.", (numIterations*ddtOffsetCentiPeriods)/ddtRangeCentiPeriods) t.Logf("t0=%s", t0) for i := 0; i < numIterations; i++ { // `ddt` is the next step to take in fake time ddt := time.Duration(rand.Intn(ddtRangeCentiPeriods)-ddtOffsetCentiPeriods) * samplingPeriod / 100 t1 = t1.Add(ddt) diff := t1.Sub(t0) if diff > dt { dt = diff } clk.SetTime(t1) saw.Set(1) expectedCount := int64(dt / samplingPeriod) actualCount, err := getHistogramCount(regs, samplesHistName) if err != nil { t.Fatalf("For t0=%s, t1=%s, failed to getHistogramCount: %#+v", t0, t1, err) } t.Logf("For i=%d, ddt=%s, t1=%s, diff=%s, dt=%s, count=%d", i, ddt, t1, diff, dt, actualCount) if expectedCount != actualCount { t.Errorf("For i=%d, t0=%s, ddt=%s, t1=%s, expectedCount=%d, actualCount=%d", i, t0, ddt, t1, expectedCount, actualCount) } } } /* getHistogramCount returns the count of the named histogram */ func getHistogramCount(regs Registerables, metricName string) (int64, error) { considered := []string{} mfs, err := legacyregistry.DefaultGatherer.Gather() if err != nil { return 0, fmt.Errorf("failed to gather metrics: %s", err) } for _, mf := range mfs { thisName := mf.GetName() if thisName != metricName { considered = append(considered, thisName) continue } metric := mf.GetMetric()[0] hist := metric.GetHistogram() if hist == nil { return 0, fmt.Errorf("dto.Metric has nil Histogram") } if hist.SampleCount == nil { return 0, fmt.Errorf("dto.Histogram has nil SampleCount") } return int64(*hist.SampleCount), nil } return 0, fmt.Errorf("not found, considered=%#+v", considered) } </ins>

Discussion:
<!-- Please only use this template for submitting enhancement requests --What would you like to be : Better testing of monotonic time in Why is this needed:
/sig api-machinery
/triage accepted
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/triage accepted