diff --git a/src/test/java/org/apache/datasketches/sampling/ReservoirCrossLanguageTest.java b/src/test/java/org/apache/datasketches/sampling/ReservoirCrossLanguageTest.java
index 717874a93..781fbebca 100644
--- a/src/test/java/org/apache/datasketches/sampling/ReservoirCrossLanguageTest.java
+++ b/src/test/java/org/apache/datasketches/sampling/ReservoirCrossLanguageTest.java
@@ -22,10 +22,12 @@
 import org.apache.datasketches.common.ArrayOfDoublesSerDe;
 import org.apache.datasketches.common.ArrayOfLongsSerDe;
 import org.apache.datasketches.common.ArrayOfStringsSerDe;
+import org.apache.datasketches.common.ResizeFactor;
 import org.testng.annotations.Test;
 
 import java.io.IOException;
 import java.nio.file.Files;
+import java.util.ArrayList;
 
 import static org.apache.datasketches.common.TestUtil.GENERATE_JAVA_FILES;
 import static org.apache.datasketches.common.TestUtil.javaPath;
@@ -74,7 +76,7 @@ public void generateReservoirLongsSketchSampling() throws IOException {
       final ReservoirLongsSketch sk = ReservoirLongsSketch.getInstance(
           predeterminedSamples,
           n,
-          org.apache.datasketches.common.ResizeFactor.X8,
+          ResizeFactor.X8,
           k
       );
 
@@ -83,6 +85,56 @@ public void generateReservoirLongsSketchSampling() throws IOException {
     }
   }
 
+  @Test(groups = {GENERATE_JAVA_FILES})
+  public void generateReservoirLongsUnionEmpty() throws IOException {
+    int maxK = 128;
+    ReservoirLongsUnion union = ReservoirLongsUnion.newInstance(maxK);
+
+    Files.newOutputStream(javaPath.resolve("reservoir_longs_union_empty_maxk" + maxK + "_java.sk"))
+        .write(union.toByteArray());
+  }
+
+  @Test(groups = {GENERATE_JAVA_FILES})
+  public void generateReservoirLongsUnionExact() throws IOException {
+    int maxK = 128;
+    int[] nArr = {1, 10, 32, 100, 128};
+
+    for (int n : nArr) {
+      ReservoirLongsUnion union = ReservoirLongsUnion.newInstance(maxK);
+      for (int i = 0; i < n; i++) {
+        union.update(i);
+      }
+      Files.newOutputStream(javaPath.resolve("reservoir_longs_union_exact_n" + n + "_maxk" + maxK + "_java.sk"))
+          .write(union.toByteArray());
+    }
+  }
+
+  @Test(groups = {GENERATE_JAVA_FILES})
+  public void generateReservoirLongsUnionSampling() throws IOException {
+    int[] maxKArr = {32, 64, 128};
+    long n = 1000;
+
+    for (int maxK : maxKArr) {
+      long[] predeterminedSamples = new long[maxK];
+      for (int i = 0; i < maxK; i++) {
+        predeterminedSamples[i] = i * 2;
+      }
+
+      ReservoirLongsSketch sk = ReservoirLongsSketch.getInstance(
+          predeterminedSamples,
+          n,
+          ResizeFactor.X8,
+          maxK
+      );
+
+      ReservoirLongsUnion union = ReservoirLongsUnion.newInstance(maxK);
+      union.update(sk);
+
+      Files.newOutputStream(javaPath.resolve("reservoir_longs_union_sampling_n" + n + "_maxk" + maxK + "_java.sk"))
+          .write(union.toByteArray());
+    }
+  }
+
   @Test(groups = {GENERATE_JAVA_FILES})
   public void generateReservoirItemsSketchLongEmpty() throws IOException {
     final int k = 128;
@@ -121,7 +173,7 @@ public void generateReservoirItemsSketchLongSampling() throws IOException {
       final ReservoirItemsSketch<Long> sk = ReservoirItemsSketch.newInstance(
           predeterminedSamples,
           n,
-          org.apache.datasketches.common.ResizeFactor.X8,
+          ResizeFactor.X8,
           k
       );
 
@@ -168,7 +220,7 @@ public void generateReservoirItemsSketchDoubleSampling() throws IOException {
       final ReservoirItemsSketch<Double> sk = ReservoirItemsSketch.newInstance(
           predeterminedSamples,
           n,
-          org.apache.datasketches.common.ResizeFactor.X8,
+          ResizeFactor.X8,
           k
       );
 
@@ -215,7 +267,7 @@ public void generateReservoirItemsSketchStringSampling() throws IOException {
       final ReservoirItemsSketch<String> sk = ReservoirItemsSketch.newInstance(
           predeterminedSamples,
           n,
-          org.apache.datasketches.common.ResizeFactor.X8,
+          ResizeFactor.X8,
           k
       );
 
@@ -223,4 +275,154 @@ public void generateReservoirItemsSketchStringSampling() throws IOException {
           .write(sk.toByteArray(new ArrayOfStringsSerDe()));
     }
   }
+
+  @Test(groups = {GENERATE_JAVA_FILES})
+  public void generateReservoirItemsUnionLongEmpty() throws IOException {
+    int maxK = 128;
+    ReservoirItemsUnion<Long> union = ReservoirItemsUnion.newInstance(maxK);
+
+    Files.newOutputStream(javaPath.resolve("reservoir_items_union_long_empty_maxk" + maxK + "_java.sk"))
+        .write(union.toByteArray(new ArrayOfLongsSerDe()));
+  }
+
+  @Test(groups = {GENERATE_JAVA_FILES})
+  public void generateReservoirItemsUnionLongExact() throws IOException {
+    int maxK = 128;
+    int[] nArr = {1, 10, 32, 100, 128};
+
+    for (int n : nArr) {
+      ReservoirItemsUnion<Long> union = ReservoirItemsUnion.newInstance(maxK);
+      for (int i = 0; i < n; i++) {
+        union.update((long) i);
+      }
+      Files.newOutputStream(javaPath.resolve("reservoir_items_union_long_exact_n" + n + "_maxk" + maxK + "_java.sk"))
+          .write(union.toByteArray(new ArrayOfLongsSerDe()));
+    }
+  }
+
+  @Test(groups = {GENERATE_JAVA_FILES})
+  public void generateReservoirItemsUnionLongSampling() throws IOException {
+    int[] maxKArr = {32, 64, 128};
+    long n = 1000;
+
+    for (int maxK : maxKArr) {
+      ArrayList<Long> predeterminedSamples = new ArrayList<>();
+      for (int i = 0; i < maxK; i++) {
+        predeterminedSamples.add((long) (i * 2));
+      }
+
+      ReservoirItemsSketch<Long> sk = ReservoirItemsSketch.newInstance(
+          predeterminedSamples,
+          n,
+          ResizeFactor.X8,
+          maxK
+      );
+
+      ReservoirItemsUnion<Long> union = ReservoirItemsUnion.newInstance(maxK);
+      union.update(sk);
+
+      Files.newOutputStream(javaPath.resolve("reservoir_items_union_long_sampling_n" + n + "_maxk" + maxK + "_java.sk"))
+          .write(union.toByteArray(new ArrayOfLongsSerDe()));
+    }
+  }
+
+  @Test(groups = {GENERATE_JAVA_FILES})
+  public void generateReservoirItemsUnionDoubleEmpty() throws IOException {
+    int maxK = 128;
+    ReservoirItemsUnion<Double> union = ReservoirItemsUnion.newInstance(maxK);
+
+    Files.newOutputStream(javaPath.resolve("reservoir_items_union_double_empty_maxk" + maxK + "_java.sk"))
+        .write(union.toByteArray(new ArrayOfDoublesSerDe()));
+  }
+
+  @Test(groups = {GENERATE_JAVA_FILES})
+  public void generateReservoirItemsUnionDoubleExact() throws IOException {
+    int maxK = 128;
+    int[] nArr = {1, 10, 32, 100, 128};
+
+    for (int n : nArr) {
+      ReservoirItemsUnion<Double> union = ReservoirItemsUnion.newInstance(maxK);
+      for (int i = 0; i < n; i++) {
+        union.update((double) i);
+      }
+      Files.newOutputStream(javaPath.resolve("reservoir_items_union_double_exact_n" + n + "_maxk" + maxK + "_java.sk"))
+          .write(union.toByteArray(new ArrayOfDoublesSerDe()));
+    }
+  }
+
+  @Test(groups = {GENERATE_JAVA_FILES})
+  public void generateReservoirItemsUnionDoubleSampling() throws IOException {
+    int[] maxKArr = {32, 64, 128};
+    long n = 1000;
+
+    for (int maxK : maxKArr) {
+      ArrayList<Double> predeterminedSamples = new ArrayList<>();
+      for (int i = 0; i < maxK; i++) {
+        predeterminedSamples.add((double) (i * 2));
+      }
+
+      ReservoirItemsSketch<Double> sk = ReservoirItemsSketch.newInstance(
+          predeterminedSamples,
+          n,
+          ResizeFactor.X8,
+          maxK
+      );
+
+      ReservoirItemsUnion<Double> union = ReservoirItemsUnion.newInstance(maxK);
+      union.update(sk);
+
+      Files.newOutputStream(javaPath.resolve("reservoir_items_union_double_sampling_n" + n + "_maxk" + maxK + "_java.sk"))
+          .write(union.toByteArray(new ArrayOfDoublesSerDe()));
+    }
+  }
+
+  @Test(groups = {GENERATE_JAVA_FILES})
+  public void generateReservoirItemsUnionStringEmpty() throws IOException {
+    int maxK = 128;
+    ReservoirItemsUnion<String> union = ReservoirItemsUnion.newInstance(maxK);
+
+    Files.newOutputStream(javaPath.resolve("reservoir_items_union_string_empty_maxk" + maxK + "_java.sk"))
+        .write(union.toByteArray(new ArrayOfStringsSerDe()));
+  }
+
+  @Test(groups = {GENERATE_JAVA_FILES})
+  public void generateReservoirItemsUnionStringExact() throws IOException {
+    int maxK = 128;
+    int[] nArr = {1, 10, 32, 100, 128};
+
+    for (int n : nArr) {
+      ReservoirItemsUnion<String> union = ReservoirItemsUnion.newInstance(maxK);
+      for (int i = 0; i < n; i++) {
+        union.update("item" + i);
+      }
+      Files.newOutputStream(javaPath.resolve("reservoir_items_union_string_exact_n" + n + "_maxk" + maxK + "_java.sk"))
+          .write(union.toByteArray(new ArrayOfStringsSerDe()));
+    }
+  }
+
+  @Test(groups = {GENERATE_JAVA_FILES})
+  public void generateReservoirItemsUnionStringSampling() throws IOException {
+    int[] maxKArr = {32, 64, 128};
+    long n = 1000;
+
+    for (int maxK : maxKArr) {
+      ArrayList<String> predeterminedSamples = new ArrayList<>();
+      for (int i = 0; i < maxK; i++) {
+        predeterminedSamples.add("item" + (i * 2));
+      }
+
+      ReservoirItemsSketch<String> sk = ReservoirItemsSketch.newInstance(
+          predeterminedSamples,
+          n,
+          ResizeFactor.X8,
+          maxK
+      );
+
+      ReservoirItemsUnion<String> union = ReservoirItemsUnion.newInstance(maxK);
+      union.update(sk);
+
+      Files.newOutputStream(javaPath.resolve("reservoir_items_union_string_sampling_n" + n + "_maxk" + maxK + "_java.sk"))
+          .write(union.toByteArray(new ArrayOfStringsSerDe()));
+    }
+  }
 }