diff --git a/src/test/java/com/uber/cadence/client/ActivityCompletionExceptionTest.java b/src/test/java/com/uber/cadence/client/ActivityCompletionExceptionTest.java
new file mode 100644
index 000000000..9c6665dc3
--- /dev/null
+++ b/src/test/java/com/uber/cadence/client/ActivityCompletionExceptionTest.java
@@ -0,0 +1,114 @@
+/**
+ * Copyright 2012-2016 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * <p>Modifications copyright (C) 2017 Uber Technologies, Inc.
+ *
+ * <p>Licensed under the Apache License, Version 2.0 (the "License"). You may not use this file
+ * except in compliance with the License. A copy of the License is located at
+ *
+ * <p>http://aws.amazon.com/apache2.0
+ *
+ * <p>or in the "license" file accompanying this file. This file 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 com.uber.cadence.client;
+
+import static junit.framework.TestCase.*;
+import static org.mockito.Mockito.*;
+
+import com.uber.cadence.WorkflowExecution;
+import com.uber.cadence.activity.ActivityTask;
+import org.junit.Before;
+import org.junit.Test;
+
+public class ActivityCompletionExceptionTest {
+
+  private ActivityTask mockTask;
+  private WorkflowExecution mockExecution;
+
+  @Before
+  public void setUp() {
+    // Set up mock objects for testing
+    mockTask = mock(ActivityTask.class);
+    mockExecution = mock(WorkflowExecution.class);
+
+    when(mockTask.getWorkflowExecution()).thenReturn(mockExecution);
+    when(mockTask.getActivityType()).thenReturn("TestActivityType");
+    when(mockTask.getActivityId()).thenReturn("TestActivityId");
+  }
+
+  @Test
+  public void testConstructorWithActivityTask() {
+    ActivityCompletionException exception = new ActivityCompletionException(mockTask);
+
+    assertEquals(mockExecution, exception.getExecution());
+    assertEquals("TestActivityType", exception.getActivityType());
+    assertEquals("TestActivityId", exception.getActivityId());
+    assertNull(exception.getCause());
+  }
+
+  @Test
+  public void testConstructorWithActivityTaskAndCause() {
+    Throwable cause = new Throwable("TestCause");
+    ActivityCompletionException exception = new ActivityCompletionException(mockTask, cause);
+
+    assertEquals(mockExecution, exception.getExecution());
+    assertEquals("TestActivityType", exception.getActivityType());
+    assertEquals("TestActivityId", exception.getActivityId());
+    assertEquals(cause, exception.getCause());
+  }
+
+  @Test
+  public void testConstructorWithActivityIdAndCause() {
+    Throwable cause = new Throwable("TestCause");
+    ActivityCompletionException exception =
+        new ActivityCompletionException("TestActivityId", cause);
+
+    assertNull(exception.getExecution());
+    assertNull(exception.getActivityType());
+    assertEquals("TestActivityId", exception.getActivityId());
+    assertEquals(cause, exception.getCause());
+  }
+
+  @Test
+  public void testConstructorWithCauseOnly() {
+    Throwable cause = new Throwable("TestCause");
+    ActivityCompletionException exception = new ActivityCompletionException(cause);
+
+    assertNull(exception.getExecution());
+    assertNull(exception.getActivityType());
+    assertNull(exception.getActivityId());
+    assertEquals(cause, exception.getCause());
+  }
+
+  @Test
+  public void testDefaultConstructor() {
+    ActivityCompletionException exception = new ActivityCompletionException();
+
+    assertNull(exception.getExecution());
+    assertNull(exception.getActivityType());
+    assertNull(exception.getActivityId());
+    assertNull(exception.getCause());
+  }
+
+  @Test
+  public void testExceptionMessageWithActivityTaskAndCause() {
+    Throwable cause = new Throwable("TestCause");
+    ActivityCompletionException exception = new ActivityCompletionException(mockTask, cause);
+
+    String expectedMessage =
+        "Execution=" + mockExecution + ", ActivityType=TestActivityType, ActivityID=TestActivityId";
+    assertEquals(expectedMessage, exception.getMessage());
+  }
+
+  @Test
+  public void testExceptionMessageWithActivityIdAndCause() {
+    Throwable cause = new Throwable("TestCause");
+    ActivityCompletionException exception =
+        new ActivityCompletionException("TestActivityId", cause);
+
+    String expectedMessage = "ActivityIdTestActivityId";
+    assertEquals(expectedMessage, exception.getMessage());
+  }
+}