add test that iterators over PaginatedStore and UnboundedSizeDenseStore are equivalent

Author: richardstartin

src/test/java/com/datadoghq/sketch/ddsketch/store/PaginatedStoreTest.java

@@ -1,5 +1,17 @@
 package com.datadoghq.sketch.ddsketch.store;
 
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+import java.util.Iterator;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+
 public class PaginatedStoreTest extends ExhaustiveStoreTest {
 
 
@@ -19,4 +31,38 @@ void testMergingExtremeValues() {
         // PaginatedStore is not meant to be used with values that are extremely far from one another as it
         // would allocate an excessively large array.
     }
+
+    public static Stream<Arguments> affineTransformations() {
+        return Stream.of(
+                Arguments.of(1, 0),
+                Arguments.of(127, 1),
+                Arguments.of(128, 0),
+                Arguments.of(128, 1),
+                Arguments.of(129, 0),
+                Arguments.of(129, 1),
+                Arguments.of(-127, 1),
+                Arguments.of(-128, 0),
+                Arguments.of(-128, 1),
+                Arguments.of(-129, 0),
+                Arguments.of(-129, 1)
+        );
+    }
+
+    @ParameterizedTest
+    @MethodSource("affineTransformations")
+    public void shouldBeEquivalentToUnboundedSizeDenseStore(int m, int c) {
+        Store paginatedStore = newStore();
+        UnboundedSizeDenseStore denseStore = new UnboundedSizeDenseStore();
+        IntStream.range(0, 1000).map(x -> m * x + c).forEach(x -> {
+            paginatedStore.add(x);
+            denseStore.add(x);
+        });
+        Iterator<Bin> pit = paginatedStore.getAscendingIterator();
+        Iterator<Bin> dit = denseStore.getAscendingIterator();
+        while (pit.hasNext() && dit.hasNext()) {
+            assertEquals(dit.next().getIndex(), pit.next().getIndex());
+        }
+        assertFalse(pit.hasNext());
+        assertFalse(dit.hasNext());
+    }
 }