1 files changed, 94 insertions, 0 deletions
diff --git a/kamon-core-tests/src/test/scala/kamon/metric/HistogramSpec.scala b/kamon-core-tests/src/test/scala/kamon/metric/HistogramSpec.scala
new file mode 100644
index 00000000..f0ea1292
--- /dev/null
+++ b/kamon-core-tests/src/test/scala/kamon/metric/HistogramSpec.scala
@@ -0,0 +1,94 @@
+package kamon.metric
+
+import kamon.Kamon
+import org.scalatest.{Matchers, WordSpec}
+import MeasurementUnit._
+
+
+class HistogramSpec extends WordSpec with Matchers {
+  import HistogramTestHelper.HistogramMetricSyntax
+
+  "a Histogram" should {
+    "record values and reset internal state when a snapshot is taken" in {
+      val histogram = Kamon.histogram("test", unit = time.nanoseconds)
+      histogram.record(100)
+      histogram.record(150, 998)
+      histogram.record(200)
+
+      val distribution = histogram.distribution()
+      distribution.min shouldBe(100)
+      distribution.max shouldBe(200)
+      distribution.count shouldBe(1000)
+      distribution.buckets.length shouldBe 3
+      distribution.buckets.map(b => (b.value, b.frequency)) should contain.allOf(
+        (100 -> 1),
+        (150 -> 998),
+        (200 -> 1)
+      )
+
+      val emptyDistribution = histogram.distribution()
+      emptyDistribution.min shouldBe(0)
+      emptyDistribution.max shouldBe(0)
+      emptyDistribution.count shouldBe(0)
+      emptyDistribution.buckets.length shouldBe 0
+    }
+
+    "accept a smallest discernible value configuration" in {
+      // The lowestDiscernibleValue gets rounded down to the closest power of 2, so, here it will be 64.
+      val histogram = Kamon.histogram("test-lowest-discernible-value", unit = time.nanoseconds, dynamicRange = DynamicRange.Fine.withLowestDiscernibleValue(100))
+      histogram.record(100)
+      histogram.record(200)
+      histogram.record(300)
+      histogram.record(1000)
+      histogram.record(2000)
+      histogram.record(3000)
+
+      val distribution = histogram.distribution()
+      distribution.min shouldBe(64)
+      distribution.max shouldBe(2944)
+      distribution.count shouldBe(6)
+      distribution.buckets.length shouldBe 6
+      distribution.buckets.map(b => (b.value, b.frequency)) should contain.allOf(
+        (64 -> 1),
+        (192 -> 1),
+        (256 -> 1),
+        (960 -> 1),
+        (1984 -> 1),
+        (2944 -> 1)
+      )
+    }
+
+    "[private api] record values and optionally keep the internal state when a snapshot is taken" in {
+      val histogram = Kamon.histogram("test", unit = time.nanoseconds)
+      histogram.record(100)
+      histogram.record(150, 998)
+      histogram.record(200)
+
+      val distribution = {
+        histogram.distribution(resetState = false) // first one gets discarded
+        histogram.distribution(resetState = false)
+      }
+
+      distribution.min shouldBe(100)
+      distribution.max shouldBe(200)
+      distribution.count shouldBe(1000)
+      distribution.buckets.length shouldBe 3
+      distribution.buckets.map(b => (b.value, b.frequency)) should contain.allOf(
+        (100 -> 1),
+        (150 -> 998),
+        (200 -> 1)
+      )
+    }
+  }
+}
+
+object HistogramTestHelper {
+
+  implicit class HistogramMetricSyntax(metric: HistogramMetric) {
+    def distribution(resetState: Boolean = true): Distribution =
+      metric.refine(Map.empty[String, String]) match {
+        case h: AtomicHdrHistogram  => h.snapshot(resetState).distribution
+        case h: HdrHistogram        => h.snapshot(resetState).distribution
+      }
+  }
+}