dt = diff
		}
		clk.SetTime(t1)
		tro.Set(1)
		expectedCount := int64(dt / samplingPeriod)
		actualCount, err := getHistogramCount(registry, histogramName)
		if err != nil && !(err == errMetricNotFound && expectedCount == 0) {
			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)