Add test case for quantile in zero-bucket

Author: JonasKunz

libs/exponential-histogram/src/test/java/org/elasticsearch/exponentialhistogram/QuantileAccuracyTests.java

@@ -27,6 +27,7 @@
 import java.util.stream.IntStream;
 
 import static org.hamcrest.Matchers.closeTo;
+import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.lessThan;
 import static org.hamcrest.Matchers.notANumber;
 
@@ -68,6 +69,13 @@ public void testBasicSmall() {
         assertThat(maxError, lessThan(0.000001));
     }
 
+    public void testPercentileOverlapsZeroBucket() {
+        ExponentialHistogram histo = ExponentialHistogramGenerator.createFor(-1, 0, 1);
+        assertThat(ExponentialHistogramQuantile.getQuantile(histo, 0.5), equalTo(0.0));
+        assertThat(ExponentialHistogramQuantile.getQuantile(histo, 0.375), closeTo(-0.5, 0.000001));
+        assertThat(ExponentialHistogramQuantile.getQuantile(histo, 0.625), closeTo(0.5, 0.000001));
+    }
+
     public void testBigJump() {
         double[] values = DoubleStream.concat(IntStream.range(0, 18).mapToDouble(Double::valueOf), DoubleStream.of(1_000_000.0)).toArray();