Quantize expected samples the same as Prom query

Signed-off-by: Tom Wilkie <tom.wilkie@gmail.com>

Author: bboreham

pkg/test/case.go

@@ -15,4 +15,5 @@ type Case interface {
 
 	Query(ctx context.Context, client v1.API, selectors string, start time.Time, duration time.Duration) ([]model.SamplePair, error)
 	ExpectedValueAt(time.Time) float64
+	Quantized(time.Duration) time.Duration
 }

pkg/test/runner.go

@@ -212,7 +212,7 @@ func (r *Runner) runRandomTest() {
 		}
 	}
 
-	expectedNumSamples := int(duration / r.cfg.ScrapeInterval)
+	expectedNumSamples := int(tc.Quantized(duration) / r.cfg.ScrapeInterval)
 	if !epsilonCorrect(float64(len(pairs)), float64(expectedNumSamples), r.cfg.samplesEpsilon) {
 		log.Errorf("Expected %d samples, got %d", expectedNumSamples, len(pairs))
 		failures = true

pkg/test/simple.go

@@ -71,3 +71,7 @@ func (tc *simpleTestCase) Query(ctx context.Context, client v1.API, selectors st
 	}
 	return result, nil
 }
+
+func (tc *simpleTestCase) Quantized(duration time.Duration) time.Duration {
+	return duration.Truncate(time.Minute)
+}