fill out missing test coverage for druid-stats, druid-momentsketch, druid-tdigestsketch postaggs (#9740)

* postagg test coverage for druid-stats, druid-momentsketch, druid-tdigestsketch and fixes

* style fixes

* fix comparator for TDigestQuantilePostAggregator

extensions-contrib/momentsketch/pom.xml

@@ -94,6 +94,11 @@
             <artifactId>easymock</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>nl.jqno.equalsverifier</groupId>
+            <artifactId>equalsverifier</artifactId>
+            <scope>test</scope>
+        </dependency>
         <dependency>
             <groupId>org.apache.druid</groupId>
             <artifactId>druid-core</artifactId>

extensions-contrib/momentsketch/src/main/java/org/apache/druid/query/aggregation/momentsketch/aggregator/MomentSketchMaxPostAggregator.java

@@ -22,7 +22,7 @@ package org.apache.druid.query.aggregation.momentsketch.aggregator;
 import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.google.common.base.Preconditions;
-import org.apache.druid.java.util.common.IAE;
+import com.google.common.primitives.Doubles;
 import org.apache.druid.query.aggregation.AggregatorFactory;
 import org.apache.druid.query.aggregation.PostAggregator;
 import org.apache.druid.query.aggregation.momentsketch.MomentSketchWrapper;
@@ -71,9 +71,9 @@ public class MomentSketchMaxPostAggregator implements PostAggregator
   }
 
   @Override
-  public Comparator<double[]> getComparator()
+  public Comparator<Double> getComparator()
   {
-    throw new IAE("Comparing arrays of quantiles is not supported");
+    return Doubles::compare;
   }
 
   @Override

extensions-contrib/momentsketch/src/main/java/org/apache/druid/query/aggregation/momentsketch/aggregator/MomentSketchMinPostAggregator.java

@@ -22,7 +22,7 @@ package org.apache.druid.query.aggregation.momentsketch.aggregator;
 import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.google.common.base.Preconditions;
-import org.apache.druid.java.util.common.IAE;
+import com.google.common.primitives.Doubles;
 import org.apache.druid.query.aggregation.AggregatorFactory;
 import org.apache.druid.query.aggregation.PostAggregator;
 import org.apache.druid.query.aggregation.momentsketch.MomentSketchWrapper;
@@ -70,9 +70,9 @@ public class MomentSketchMinPostAggregator implements PostAggregator
   }
 
   @Override
-  public Comparator<double[]> getComparator()
+  public Comparator<Double> getComparator()
   {
-    throw new IAE("Comparing arrays of quantiles is not supported");
+    return Doubles::compare;
   }
 
   @Override

extensions-contrib/momentsketch/src/test/java/org/apache/druid/query/aggregation/momentsketch/aggregator/MomentSketchMaxPostAggregatorTest.java

@@ -0,0 +1,68 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.query.aggregation.momentsketch.aggregator;
+
+import nl.jqno.equalsverifier.EqualsVerifier;
+import org.apache.druid.jackson.DefaultObjectMapper;
+import org.apache.druid.query.aggregation.PostAggregator;
+import org.apache.druid.query.aggregation.post.ConstantPostAggregator;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class MomentSketchMaxPostAggregatorTest
+{
+  @Test
+  public void testSerde() throws Exception
+  {
+    MomentSketchMaxPostAggregator there =
+        new MomentSketchMaxPostAggregator("post", new ConstantPostAggregator("", 100));
+
+    DefaultObjectMapper mapper = new DefaultObjectMapper();
+    MomentSketchMaxPostAggregator andBackAgain = mapper.readValue(
+        mapper.writeValueAsString(there),
+        MomentSketchMaxPostAggregator.class
+    );
+
+    Assert.assertEquals(there, andBackAgain);
+    Assert.assertArrayEquals(there.getCacheKey(), andBackAgain.getCacheKey());
+    Assert.assertEquals(there.getDependentFields(), andBackAgain.getDependentFields());
+  }
+
+  @Test
+  public void testToString()
+  {
+    PostAggregator postAgg =
+        new MomentSketchMaxPostAggregator("post", new ConstantPostAggregator("", 100));
+
+    Assert.assertEquals(
+        "MomentSketchMaxPostAggregator{name='post', field=ConstantPostAggregator{name='', constantValue=100}}",
+        postAgg.toString()
+    );
+  }
+
+  @Test
+  public void testEquals()
+  {
+    EqualsVerifier.forClass(MomentSketchMaxPostAggregator.class)
+                  .withNonnullFields("name", "field")
+                  .usingGetClass()
+                  .verify();
+  }
+}

extensions-contrib/momentsketch/src/test/java/org/apache/druid/query/aggregation/momentsketch/aggregator/MomentSketchMinPostAggregatorTest.java

@@ -0,0 +1,68 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.query.aggregation.momentsketch.aggregator;
+
+import nl.jqno.equalsverifier.EqualsVerifier;
+import org.apache.druid.jackson.DefaultObjectMapper;
+import org.apache.druid.query.aggregation.PostAggregator;
+import org.apache.druid.query.aggregation.post.ConstantPostAggregator;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class MomentSketchMinPostAggregatorTest
+{
+  @Test
+  public void testSerde() throws Exception
+  {
+    MomentSketchMinPostAggregator there =
+        new MomentSketchMinPostAggregator("post", new ConstantPostAggregator("", 100));
+
+    DefaultObjectMapper mapper = new DefaultObjectMapper();
+    MomentSketchMinPostAggregator andBackAgain = mapper.readValue(
+        mapper.writeValueAsString(there),
+        MomentSketchMinPostAggregator.class
+    );
+
+    Assert.assertEquals(there, andBackAgain);
+    Assert.assertArrayEquals(there.getCacheKey(), andBackAgain.getCacheKey());
+    Assert.assertEquals(there.getDependentFields(), andBackAgain.getDependentFields());
+  }
+
+  @Test
+  public void testToString()
+  {
+    PostAggregator postAgg =
+        new MomentSketchMinPostAggregator("post", new ConstantPostAggregator("", 100));
+
+    Assert.assertEquals(
+        "MomentSketchMinPostAggregator{name='post', field=ConstantPostAggregator{name='', constantValue=100}}",
+        postAgg.toString()
+    );
+  }
+
+  @Test
+  public void testEquals()
+  {
+    EqualsVerifier.forClass(MomentSketchMinPostAggregator.class)
+                  .withNonnullFields("name", "field")
+                  .usingGetClass()
+                  .verify();
+  }
+}

extensions-contrib/momentsketch/src/test/java/org/apache/druid/query/aggregation/momentsketch/aggregator/MomentSketchQuantilePostAggregatorTest.java

@@ -0,0 +1,83 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.query.aggregation.momentsketch.aggregator;
+
+import nl.jqno.equalsverifier.EqualsVerifier;
+import org.apache.druid.jackson.DefaultObjectMapper;
+import org.apache.druid.java.util.common.IAE;
+import org.apache.druid.query.aggregation.PostAggregator;
+import org.apache.druid.query.aggregation.post.ConstantPostAggregator;
+import org.junit.Assert;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+public class MomentSketchQuantilePostAggregatorTest
+{
+  @Rule
+  public ExpectedException expectedException = ExpectedException.none();
+
+  @Test
+  public void testSerde() throws Exception
+  {
+    MomentSketchQuantilePostAggregator there =
+        new MomentSketchQuantilePostAggregator("post", new ConstantPostAggregator("", 100), new double[]{0.25, 0.75});
+
+    DefaultObjectMapper mapper = new DefaultObjectMapper();
+    MomentSketchQuantilePostAggregator andBackAgain = mapper.readValue(
+        mapper.writeValueAsString(there),
+        MomentSketchQuantilePostAggregator.class
+    );
+
+    Assert.assertEquals(there, andBackAgain);
+    Assert.assertArrayEquals(there.getCacheKey(), andBackAgain.getCacheKey());
+    Assert.assertEquals(there.getDependentFields(), andBackAgain.getDependentFields());
+  }
+
+  @Test
+  public void testToString()
+  {
+    PostAggregator postAgg =
+        new MomentSketchQuantilePostAggregator("post", new ConstantPostAggregator("", 100), new double[]{0.25, 0.75});
+
+    Assert.assertEquals(
+        "MomentSketchQuantilePostAggregator{name='post', field=ConstantPostAggregator{name='', constantValue=100}, fractions=[0.25, 0.75]}",
+        postAgg.toString()
+    );
+  }
+
+  @Test
+  public void testComparator()
+  {
+    expectedException.expect(IAE.class);
+    expectedException.expectMessage("Comparing arrays of quantiles is not supported");
+    PostAggregator postAgg =
+        new MomentSketchQuantilePostAggregator("post", new ConstantPostAggregator("", 100), new double[]{0.25, 0.75});
+    postAgg.getComparator();
+  }
+  @Test
+  public void testEquals()
+  {
+    EqualsVerifier.forClass(MomentSketchQuantilePostAggregator.class)
+                  .withNonnullFields("name", "field", "fractions")
+                  .usingGetClass()
+                  .verify();
+  }
+}

extensions-contrib/tdigestsketch/pom.xml

@@ -147,6 +147,11 @@
       <artifactId>easymock</artifactId>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>nl.jqno.equalsverifier</groupId>
+      <artifactId>equalsverifier</artifactId>
+      <scope>test</scope>
+    </dependency>
     <dependency>
       <groupId>org.apache.druid</groupId>
       <artifactId>druid-core</artifactId>

extensions-contrib/tdigestsketch/src/main/java/org/apache/druid/query/aggregation/tdigestsketch/TDigestSketchToQuantilePostAggregator.java

@@ -22,8 +22,8 @@ package org.apache.druid.query.aggregation.tdigestsketch;
 import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.google.common.base.Preconditions;
+import com.google.common.primitives.Doubles;
 import com.tdunning.math.stats.MergingDigest;
-import org.apache.druid.java.util.common.IAE;
 import org.apache.druid.query.aggregation.AggregatorFactory;
 import org.apache.druid.query.aggregation.PostAggregator;
 import org.apache.druid.query.aggregation.post.PostAggregatorIds;
@@ -40,7 +40,6 @@ import java.util.Set;
  */
 public class TDigestSketchToQuantilePostAggregator implements PostAggregator
 {
-
   private final String name;
   private final PostAggregator field;
 
@@ -87,9 +86,9 @@ public class TDigestSketchToQuantilePostAggregator implements PostAggregator
   }
 
   @Override
-  public Comparator<double[]> getComparator()
+  public Comparator<Double> getComparator()
   {
-    throw new IAE("Comparing arrays of quantiles is not supported");
+    return Doubles::compare;
   }
 
   @Override

extensions-contrib/tdigestsketch/src/test/java/org/apache/druid/query/aggregation/tdigestsketch/TDigestSketchToQuantilePostAggregatorTest.java

@@ -0,0 +1,73 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.query.aggregation.tdigestsketch;
+
+import nl.jqno.equalsverifier.EqualsVerifier;
+import org.apache.druid.jackson.DefaultObjectMapper;
+import org.apache.druid.query.aggregation.PostAggregator;
+import org.apache.druid.query.aggregation.post.ConstantPostAggregator;
+import org.junit.Assert;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+public class TDigestSketchToQuantilePostAggregatorTest
+{
+  @Rule
+  public ExpectedException expectedException = ExpectedException.none();
+
+  @Test
+  public void testSerde() throws Exception
+  {
+    TDigestSketchToQuantilePostAggregator there =
+        new TDigestSketchToQuantilePostAggregator("post", new ConstantPostAggregator("", 100), 0.5);
+
+    DefaultObjectMapper mapper = new DefaultObjectMapper();
+    TDigestSketchToQuantilePostAggregator andBackAgain = mapper.readValue(
+        mapper.writeValueAsString(there),
+        TDigestSketchToQuantilePostAggregator.class
+    );
+
+    Assert.assertEquals(there, andBackAgain);
+    Assert.assertArrayEquals(there.getCacheKey(), andBackAgain.getCacheKey());
+    Assert.assertEquals(there.getDependentFields(), andBackAgain.getDependentFields());
+  }
+
+  @Test
+  public void testToString()
+  {
+    PostAggregator postAgg =
+        new TDigestSketchToQuantilePostAggregator("post", new ConstantPostAggregator("", 100), 0.5);
+
+    Assert.assertEquals(
+        "TDigestSketchToQuantilePostAggregator{name='post', field=ConstantPostAggregator{name='', constantValue=100}, fraction=0.5}",
+        postAgg.toString()
+    );
+  }
+
+  @Test
+  public void testEquals()
+  {
+    EqualsVerifier.forClass(TDigestSketchToQuantilePostAggregator.class)
+                  .withNonnullFields("name", "field", "fraction")
+                  .usingGetClass()
+                  .verify();
+  }
+}

extensions-contrib/tdigestsketch/src/test/java/org/apache/druid/query/aggregation/tdigestsketch/TDigestSketchToQuantilesPostAggregatorTest.java

@@ -0,0 +1,90 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.query.aggregation.tdigestsketch;
+
+import nl.jqno.equalsverifier.EqualsVerifier;
+import org.apache.druid.jackson.DefaultObjectMapper;
+import org.apache.druid.java.util.common.IAE;
+import org.apache.druid.query.aggregation.PostAggregator;
+import org.apache.druid.query.aggregation.post.ConstantPostAggregator;
+import org.junit.Assert;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+public class TDigestSketchToQuantilesPostAggregatorTest
+{
+  @Rule
+  public ExpectedException expectedException = ExpectedException.none();
+
+  @Test
+  public void testSerde() throws Exception
+  {
+    TDigestSketchToQuantilesPostAggregator there =
+        new TDigestSketchToQuantilesPostAggregator("post", new ConstantPostAggregator("", 100), new double[]{0.25, 0.75});
+
+    DefaultObjectMapper mapper = new DefaultObjectMapper();
+    TDigestSketchToQuantilesPostAggregator andBackAgain = mapper.readValue(
+        mapper.writeValueAsString(there),
+        TDigestSketchToQuantilesPostAggregator.class
+    );
+
+    Assert.assertEquals(there, andBackAgain);
+    Assert.assertArrayEquals(there.getCacheKey(), andBackAgain.getCacheKey());
+    Assert.assertEquals(there.getDependentFields(), andBackAgain.getDependentFields());
+  }
+
+  @Test
+  public void testToString()
+  {
+    PostAggregator postAgg = new TDigestSketchToQuantilesPostAggregator(
+        "post",
+        new ConstantPostAggregator("", 100),
+        new double[]{0.25, 0.75}
+    );
+
+    Assert.assertEquals(
+        "TDigestSketchToQuantilesPostAggregator{name='post', field=ConstantPostAggregator{name='', constantValue=100}, fractions=[0.25, 0.75]}",
+        postAgg.toString()
+    );
+  }
+
+  @Test
+  public void testComparator()
+  {
+    expectedException.expect(IAE.class);
+    expectedException.expectMessage("Comparing arrays of quantiles is not supported");
+    PostAggregator postAgg = new TDigestSketchToQuantilesPostAggregator(
+        "post",
+        new ConstantPostAggregator("", 100),
+        new double[]{0.25, 0.75}
+    );
+    postAgg.getComparator();
+  }
+
+  @Test
+  public void testEquals()
+  {
+    EqualsVerifier.forClass(TDigestSketchToQuantilesPostAggregator.class)
+                  .withNonnullFields("name", "field", "fractions")
+                  .usingGetClass()
+                  .verify();
+  }
+}

extensions-core/stats/pom.xml

@@ -141,6 +141,11 @@
             <artifactId>easymock</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>nl.jqno.equalsverifier</groupId>
+            <artifactId>equalsverifier</artifactId>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
 </project>

extensions-core/stats/src/main/java/org/apache/druid/query/aggregation/teststats/PvaluefromZscorePostAggregator.java

@@ -79,9 +79,11 @@ public class PvaluefromZscorePostAggregator implements PostAggregator
   @Override
   public Object compute(Map<String, Object> combinedAggregators)
   {
-
-    double zScoreValue = ((Number) zScore.compute(combinedAggregators))
-        .doubleValue();
+    Object result = zScore.compute(combinedAggregators);
+    if (!(result instanceof Number)) {
+      return null;
+    }
+    double zScoreValue = ((Number) result).doubleValue();
 
     zScoreValue = Math.abs(zScoreValue);
     return 2 * (1 - cumulativeProbability(zScoreValue));
@@ -116,7 +118,7 @@ public class PvaluefromZscorePostAggregator implements PostAggregator
   }
 
   @JsonProperty
-  public PostAggregator getZscore()
+  public PostAggregator getzScore()
   {
     return zScore;
   }

extensions-core/stats/src/main/java/org/apache/druid/query/aggregation/teststats/ZtestPostAggregator.java

@@ -99,11 +99,18 @@ public class ZtestPostAggregator implements PostAggregator
   @Override
   public Object compute(Map<String, Object> combinedAggregators)
   {
+    Object sc1 = successCount1.compute(combinedAggregators);
+    Object ss1 = sample1Size.compute(combinedAggregators);
+    Object sc2 = successCount2.compute(combinedAggregators);
+    Object ss2 = sample2Size.compute(combinedAggregators);
+    if (!(sc1 instanceof Number) || !(sc2 instanceof Number) || !(ss1 instanceof Number) || !(ss2 instanceof Number)) {
+      return null;
+    }
     return zScoreTwoSamples(
-        ((Number) successCount1.compute(combinedAggregators)).doubleValue(),
-        ((Number) sample1Size.compute(combinedAggregators)).doubleValue(),
-        ((Number) successCount2.compute(combinedAggregators)).doubleValue(),
-        ((Number) sample2Size.compute(combinedAggregators)).doubleValue()
+        ((Number) sc1).doubleValue(),
+        ((Number) ss1).doubleValue(),
+        ((Number) sc2).doubleValue(),
+        ((Number) ss2).doubleValue()
     );
   }
 

extensions-core/stats/src/test/java/org/apache/druid/query/aggregation/teststats/PvaluefromZscorePostAggregatorTest.java

@@ -20,32 +20,52 @@
 package org.apache.druid.query.aggregation.teststats;
 
 import com.google.common.collect.ImmutableMap;
+import nl.jqno.equalsverifier.EqualsVerifier;
 import org.apache.druid.jackson.DefaultObjectMapper;
-import org.apache.druid.query.aggregation.post.ConstantPostAggregator;
+import org.apache.druid.query.aggregation.post.FieldAccessPostAggregator;
 import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Rule;
 import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+import java.util.HashMap;
+import java.util.Map;
 
 public class PvaluefromZscorePostAggregatorTest
 {
   PvaluefromZscorePostAggregator pvaluefromZscorePostAggregator;
-  ConstantPostAggregator zscore;
+  FieldAccessPostAggregator zscore;
+
+  @Rule
+  public ExpectedException expectedException = ExpectedException.none();
+
+  @Before
+  public void setup()
+  {
+    zscore = new FieldAccessPostAggregator("f1", "zscore");
+    pvaluefromZscorePostAggregator = new PvaluefromZscorePostAggregator("pvalue", zscore);
+  }
 
   @Test
   public void testPvaluefromZscorePostAggregator()
   {
-    zscore = new ConstantPostAggregator("zscore", -1783.8762354220219);
-
-    pvaluefromZscorePostAggregator = new PvaluefromZscorePostAggregator("pvalue", zscore);
-
-    double pvalue = ((Number) pvaluefromZscorePostAggregator.compute(ImmutableMap.of(
-        "zscore",
-        -1783.8762354220219
-    ))).doubleValue();
+    Map<String, Object> row = ImmutableMap.of("zscore", -1783.8762354220219);
+    double pvalue = ((Number) pvaluefromZscorePostAggregator.compute(row)).doubleValue();
 
     /* Assert P-value is positive and very small */
     Assert.assertTrue(pvalue >= 0 && pvalue < 0.00001);
   }
 
+  @Test
+  public void testPvaluefromNullZscorePostAggregator()
+  {
+    Map<String, Object> row = new HashMap<>();
+    row.put("zscore", null);
+    Object result = pvaluefromZscorePostAggregator.compute(row);
+    Assert.assertNull(result);
+  }
+
   @Test
   public void testSerde() throws Exception
   {
@@ -56,6 +76,25 @@ public class PvaluefromZscorePostAggregatorTest
     );
 
     Assert.assertEquals(pvaluefromZscorePostAggregator, postAggregator1);
+    Assert.assertArrayEquals(pvaluefromZscorePostAggregator.getCacheKey(), postAggregator1.getCacheKey());
+    Assert.assertEquals(pvaluefromZscorePostAggregator.getDependentFields(), postAggregator1.getDependentFields());
   }
 
+  @Test
+  public void testToString()
+  {
+    Assert.assertEquals(
+        "PvaluefromZscorePostAggregator{name='pvalue', zScore=FieldAccessPostAggregator{name='f1', fieldName='zscore'}}",
+        pvaluefromZscorePostAggregator.toString()
+    );
+  }
+
+  @Test
+  public void testEquals()
+  {
+    EqualsVerifier.forClass(PvaluefromZscorePostAggregator.class)
+                  .withNonnullFields("name", "zScore")
+                  .usingGetClass()
+                  .verify();
+  }
 }

extensions-core/stats/src/test/java/org/apache/druid/query/aggregation/teststats/ZtestPostAggregatorTest.java

@@ -19,43 +19,31 @@
 
 package org.apache.druid.query.aggregation.teststats;
 
-import com.google.common.collect.Lists;
+import nl.jqno.equalsverifier.EqualsVerifier;
 import org.apache.druid.jackson.DefaultObjectMapper;
-import org.apache.druid.query.aggregation.PostAggregator;
-import org.apache.druid.query.aggregation.post.ConstantPostAggregator;
+import org.apache.druid.query.aggregation.post.FieldAccessPostAggregator;
 import org.junit.Assert;
+import org.junit.Before;
 import org.junit.Test;
 
 import java.util.HashMap;
-import java.util.List;
 import java.util.Map;
 
 public class ZtestPostAggregatorTest
 {
+  FieldAccessPostAggregator successCount1;
+  FieldAccessPostAggregator sample1Size;
+  FieldAccessPostAggregator successCount2;
+  FieldAccessPostAggregator sample2Size;
   ZtestPostAggregator ztestPostAggregator;
 
-  @Test
-  public void testZtestPostAggregator()
+  @Before
+  public void setup()
   {
-    ConstantPostAggregator successCount1, sample1Size, successCount2, sample2Size;
-
-    successCount1 = new ConstantPostAggregator("successCountPopulation1", 39244);
-    sample1Size = new ConstantPostAggregator("sampleSizePopulation1", 394298);
-    successCount2 = new ConstantPostAggregator("successCountPopulation2", 8991275);
-    sample2Size = new ConstantPostAggregator("sampleSizePopulation2", 9385573);
-
-    List<PostAggregator> postAggregatorList;
-    postAggregatorList = Lists.newArrayList(
-        successCount1,
-        sample1Size,
-        successCount2,
-        sample2Size
-    );
-
-    Map<String, Object> metricValues = new HashMap<>();
-    for (PostAggregator pa : postAggregatorList) {
-      metricValues.put(pa.getName(), ((ConstantPostAggregator) pa).getConstantValue());
-    }
+    successCount1 = new FieldAccessPostAggregator("sc1", "successCountPopulation1");
+    sample1Size = new FieldAccessPostAggregator("ss1", "sampleSizePopulation1");
+    successCount2 = new FieldAccessPostAggregator("sc2", "successCountPopulation2");
+    sample2Size = new FieldAccessPostAggregator("ss2", "sampleSizePopulation2");
 
     ztestPostAggregator = new ZtestPostAggregator(
         "zscore",
@@ -64,14 +52,34 @@ public class ZtestPostAggregatorTest
         successCount2,
         sample2Size
     );
+  }
+
+  @Test
+  public void testZtestPostAggregator()
+  {
+    Map<String, Object> metricValues = new HashMap<>();
+
+    Object result = ztestPostAggregator.compute(metricValues);
+    Assert.assertNull(result);
+
+    metricValues.put("successCountPopulation1", 39244);
+    result = ztestPostAggregator.compute(metricValues);
+    Assert.assertNull(result);
+
+    metricValues.put("sampleSizePopulation1", 394298);
+    result = ztestPostAggregator.compute(metricValues);
+    Assert.assertNull(result);
+
+    metricValues.put("successCountPopulation2", 8991275);
+    result = ztestPostAggregator.compute(metricValues);
+    metricValues.put("sampleSizePopulation2", 9385573);
+    Assert.assertNull(result);
 
     double zscore = ((Number) ztestPostAggregator.compute(metricValues)).doubleValue();
-
-    Assert.assertEquals(-1783.8762354220219,
-                        zscore, 0.0001
-    );
+    Assert.assertEquals(-1783.8762354220219, zscore, 0.0001);
   }
 
+
   @Test
   public void testSerde() throws Exception
   {
@@ -83,5 +91,25 @@ public class ZtestPostAggregatorTest
         );
 
     Assert.assertEquals(ztestPostAggregator, postAggregator1);
+    Assert.assertArrayEquals(ztestPostAggregator.getCacheKey(), postAggregator1.getCacheKey());
+    Assert.assertEquals(ztestPostAggregator.getDependentFields(), postAggregator1.getDependentFields());
+  }
+
+  @Test
+  public void testToString()
+  {
+    Assert.assertEquals(
+        "ZtestPostAggregator{name='zscore', successCount1='FieldAccessPostAggregator{name='sc1', fieldName='successCountPopulation1'}', sample1Size='FieldAccessPostAggregator{name='ss1', fieldName='sampleSizePopulation1'}', successCount2='FieldAccessPostAggregator{name='sc2', fieldName='successCountPopulation2'}', sample2size='FieldAccessPostAggregator{name='ss2', fieldName='sampleSizePopulation2'}}",
+        ztestPostAggregator.toString()
+    );
+  }
+
+  @Test
+  public void testEquals()
+  {
+    EqualsVerifier.forClass(ZtestPostAggregator.class)
+                  .withNonnullFields("name", "successCount1", "sample1Size", "successCount2", "sample2Size")
+                  .usingGetClass()
+                  .verify();
   }
 }

extensions-core/stats/src/test/java/org/apache/druid/query/aggregation/variance/StandardDeviationPostAggregatorTest.java

@@ -0,0 +1,67 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.query.aggregation.variance;
+
+import nl.jqno.equalsverifier.EqualsVerifier;
+import org.apache.druid.jackson.DefaultObjectMapper;
+import org.apache.druid.query.aggregation.PostAggregator;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class StandardDeviationPostAggregatorTest
+{
+  @Test
+  public void testSerde() throws Exception
+  {
+    StandardDeviationPostAggregator there =
+        new StandardDeviationPostAggregator("post", "test_field", "population");
+
+    DefaultObjectMapper mapper = new DefaultObjectMapper();
+    StandardDeviationPostAggregator andBackAgain = mapper.readValue(
+        mapper.writeValueAsString(there),
+        StandardDeviationPostAggregator.class
+    );
+
+    Assert.assertEquals(there, andBackAgain);
+    Assert.assertArrayEquals(there.getCacheKey(), andBackAgain.getCacheKey());
+    Assert.assertEquals(there.getDependentFields(), andBackAgain.getDependentFields());
+  }
+
+  @Test
+  public void testToString()
+  {
+    PostAggregator postAgg =
+        new StandardDeviationPostAggregator("post", "test_field", "population");
+
+    Assert.assertEquals(
+        "StandardDeviationPostAggregator{name='post', fieldName='test_field', estimator='population', isVariancePop=true}",
+        postAgg.toString()
+    );
+  }
+
+  @Test
+  public void testEquals()
+  {
+    EqualsVerifier.forClass(StandardDeviationPostAggregator.class)
+                  .withNonnullFields("name", "fieldName")
+                  .usingGetClass()
+                  .verify();
+  }
+}

extensions-core/stats/src/test/java/org/apache/druid/query/aggregation/variance/VarianceGroupByQueryTest.java

@@ -26,6 +26,10 @@ import org.apache.druid.java.util.common.granularity.PeriodGranularity;
 import org.apache.druid.query.QueryRunner;
 import org.apache.druid.query.QueryRunnerTestHelper;
 import org.apache.druid.query.aggregation.LongSumAggregatorFactory;
+import org.apache.druid.query.aggregation.post.ConstantPostAggregator;
+import org.apache.druid.query.aggregation.post.FieldAccessPostAggregator;
+import org.apache.druid.query.aggregation.teststats.PvaluefromZscorePostAggregator;
+import org.apache.druid.query.aggregation.teststats.ZtestPostAggregator;
 import org.apache.druid.query.dimension.DefaultDimensionSpec;
 import org.apache.druid.query.groupby.GroupByQuery;
 import org.apache.druid.query.groupby.GroupByQueryConfig;
@@ -235,4 +239,82 @@ public class VarianceGroupByQueryTest extends InitializedNullHandlingTest
     results = GroupByQueryRunnerTestHelper.runQuery(factory, runner, query);
     TestHelper.assertExpectedObjects(expectedResults, results, "limitSpec");
   }
+
+  @Test
+  public void testGroupByZtestPostAgg()
+  {
+    // test postaggs from 'teststats' package in here since we've already gone to the trouble of setting up the test
+    GroupByQuery query = GroupByQuery
+        .builder()
+        .setDataSource(QueryRunnerTestHelper.DATA_SOURCE)
+        .setQuerySegmentSpec(QueryRunnerTestHelper.FIRST_TO_THIRD)
+        .setDimensions(new DefaultDimensionSpec("quality", "alias"))
+        .setAggregatorSpecs(
+            QueryRunnerTestHelper.ROWS_COUNT,
+            VarianceTestHelper.INDEX_VARIANCE_AGGR,
+            new LongSumAggregatorFactory("idx", "index")
+        )
+        .setPostAggregatorSpecs(
+            ImmutableList.of(
+                VarianceTestHelper.STD_DEV_OF_INDEX_POST_AGGR,
+                // these inputs are totally nonsensical, i just want the code path to be executed
+                new ZtestPostAggregator(
+                    "ztest",
+                    new FieldAccessPostAggregator("f1", "idx"),
+                    new ConstantPostAggregator("f2", 100000L),
+                    new FieldAccessPostAggregator("f3", "index_stddev"),
+                    new ConstantPostAggregator("f2", 100000L)
+                )
+            )
+        )
+        .setLimitSpec(new DefaultLimitSpec(OrderByColumnSpec.descending("ztest"), 1))
+        .setGranularity(QueryRunnerTestHelper.DAY_GRAN)
+        .build();
+
+    VarianceTestHelper.RowBuilder builder =
+        new VarianceTestHelper.RowBuilder(new String[]{"alias", "rows", "idx", "index_stddev", "index_var", "ztest"});
+
+    List<ResultRow> expectedResults = builder
+        .add("2011-04-01", "premium", 3L, 2900.0, 726.632270328514, 527994.4562827706, 36.54266309285626)
+        .build(query);
+
+    Iterable<ResultRow> results = GroupByQueryRunnerTestHelper.runQuery(factory, runner, query);
+    TestHelper.assertExpectedObjects(expectedResults, results, "groupBy");
+  }
+
+  @Test
+  public void testGroupByTestPvalueZscorePostAgg()
+  {
+    // test postaggs from 'teststats' package in here since we've already gone to the trouble of setting up the test
+    GroupByQuery query = GroupByQuery
+        .builder()
+        .setDataSource(QueryRunnerTestHelper.DATA_SOURCE)
+        .setQuerySegmentSpec(QueryRunnerTestHelper.FIRST_TO_THIRD)
+        .setDimensions(new DefaultDimensionSpec("quality", "alias"))
+        .setAggregatorSpecs(
+            QueryRunnerTestHelper.ROWS_COUNT,
+            VarianceTestHelper.INDEX_VARIANCE_AGGR,
+            new LongSumAggregatorFactory("idx", "index")
+        )
+        .setPostAggregatorSpecs(
+            ImmutableList.of(
+                VarianceTestHelper.STD_DEV_OF_INDEX_POST_AGGR,
+                // nonsensical inputs
+                new PvaluefromZscorePostAggregator("pvalueZscore", new FieldAccessPostAggregator("f1", "index_stddev"))
+            )
+        )
+        .setLimitSpec(new DefaultLimitSpec(OrderByColumnSpec.descending("pvalueZscore"), 1))
+        .setGranularity(QueryRunnerTestHelper.DAY_GRAN)
+        .build();
+
+    VarianceTestHelper.RowBuilder builder =
+        new VarianceTestHelper.RowBuilder(new String[]{"alias", "rows", "idx", "index_stddev", "index_var", "pvalueZscore"});
+
+    List<ResultRow> expectedResults = builder
+        .add("2011-04-01", "automotive", 1L, 135.0, 0.0, 0.0, 1.0)
+        .build(query);
+
+    Iterable<ResultRow> results = GroupByQueryRunnerTestHelper.runQuery(factory, runner, query);
+    TestHelper.assertExpectedObjects(expectedResults, results, "groupBy");
+  }
 }