Added tests for thread-pool pattern

Fixed concurrency problem in id generation of Task

thread-pool/pom.xml

@@ -14,5 +14,10 @@
       <artifactId>junit</artifactId>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>org.mockito</groupId>
+      <artifactId>mockito-core</artifactId>
+      <scope>test</scope>
+    </dependency>
   </dependencies>
 </project>

thread-pool/src/main/java/com/iluwatar/threadpool/CoffeeMakingTask.java

@@ -7,7 +7,7 @@
  */
 public class CoffeeMakingTask extends Task {
 
-  private static final int TIME_PER_CUP = 300;
+  private static final int TIME_PER_CUP = 100;
 
   public CoffeeMakingTask(int numCups) {
     super(numCups * TIME_PER_CUP);

thread-pool/src/main/java/com/iluwatar/threadpool/PotatoPeelingTask.java

@@ -7,7 +7,7 @@
  */
 public class PotatoPeelingTask extends Task {
 
-  private static final int TIME_PER_POTATO = 500;
+  private static final int TIME_PER_POTATO = 200;
 
   public PotatoPeelingTask(int numPotatoes) {
     super(numPotatoes * TIME_PER_POTATO);

thread-pool/src/main/java/com/iluwatar/threadpool/Task.java

@@ -1,19 +1,21 @@
 package com.iluwatar.threadpool;
 
+import java.util.concurrent.atomic.AtomicInteger;
+
 /**
- * 
+ *
  * Abstract base class for tasks
  *
  */
 public abstract class Task {
 
-  private static int nextId = 1;
+  private static final AtomicInteger ID_GENERATOR = new AtomicInteger();
 
   private final int id;
   private final int timeMs;
 
   public Task(final int timeMs) {
-    this.id = nextId++;
+    this.id = ID_GENERATOR.incrementAndGet();
     this.timeMs = timeMs;
   }
 

thread-pool/src/test/java/com/iluwatar/threadpool/CoffeeMakingTaskTest.java

@@ -0,0 +1,17 @@
+package com.iluwatar.threadpool;
+
+/**
+ * Date: 12/30/15 - 18:23 PM
+ *
+ * @author Jeroen Meulemeester
+ */
+public class CoffeeMakingTaskTest extends TaskTest<CoffeeMakingTask> {
+
+  /**
+   * Create a new test instance
+   */
+  public CoffeeMakingTaskTest() {
+    super(CoffeeMakingTask::new, 100);
+  }
+
+}

thread-pool/src/test/java/com/iluwatar/threadpool/PotatoPeelingTaskTest.java

@@ -0,0 +1,17 @@
+package com.iluwatar.threadpool;
+
+/**
+ * Date: 12/30/15 - 18:23 PM
+ *
+ * @author Jeroen Meulemeester
+ */
+public class PotatoPeelingTaskTest extends TaskTest<PotatoPeelingTask> {
+
+  /**
+   * Create a new test instance
+   */
+  public PotatoPeelingTaskTest() {
+    super(PotatoPeelingTask::new, 200);
+  }
+
+}

thread-pool/src/test/java/com/iluwatar/threadpool/TaskTest.java

@@ -0,0 +1,121 @@
+package com.iluwatar.threadpool;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+
+/**
+ * Date: 12/30/15 - 18:22 PM
+ *
+ * @author Jeroen Meulemeester
+ */
+public abstract class TaskTest<T extends Task> {
+
+  /**
+   * The number of tasks used during the concurrency test
+   */
+  private static final int TASK_COUNT = 128 * 1024;
+
+  /**
+   * The number of threads used during the concurrency test
+   */
+  private static final int THREAD_COUNT = 8;
+
+  /**
+   * The task factory, used to create new test items
+   */
+  private final Function<Integer, T> factory;
+
+  /**
+   * The expected time needed to run the task 1 single time, in milli seconds
+   */
+  private final int expectedExecutionTime;
+
+  /**
+   * Create a new test instance
+   *
+   * @param factory               The task factory, used to create new test items
+   * @param expectedExecutionTime The expected time needed to run the task 1 time, in milli seconds
+   */
+  public TaskTest(final Function<Integer, T> factory, final int expectedExecutionTime) {
+    this.factory = factory;
+    this.expectedExecutionTime = expectedExecutionTime;
+  }
+
+  /**
+   * Verify if the generated id is unique for each task, even if the tasks are created in separate
+   * threads
+   */
+  @Test(timeout = 10000)
+  public void testIdGeneration() throws Exception {
+    final ExecutorService service = Executors.newFixedThreadPool(THREAD_COUNT);
+
+    final List<Callable<Integer>> tasks = new ArrayList<>();
+    for (int i = 0; i < TASK_COUNT; i++) {
+      tasks.add(() -> factory.apply(1).getId());
+    }
+
+    final List<Integer> ids = service.invokeAll(tasks)
+        .stream()
+        .map(TaskTest::get)
+        .filter(Objects::nonNull)
+        .collect(Collectors.toList());
+
+    service.shutdownNow();
+
+    final long uniqueIdCount = ids.stream()
+        .distinct()
+        .count();
+
+    assertEquals(TASK_COUNT, ids.size());
+    assertEquals(TASK_COUNT, uniqueIdCount);
+
+  }
+
+  /**
+   * Verify if the time per execution of a task matches the actual time required to execute the task
+   * a given number of times
+   */
+  @Test
+  public void testTimeMs() {
+    for (int i = 0; i < 10; i++) {
+      assertEquals(this.expectedExecutionTime * i, this.factory.apply(i).getTimeMs());
+    }
+  }
+
+  /**
+   * Verify if the task has some sort of {@link T#toString()}, different from 'null'
+   */
+  @Test
+  public void testToString() {
+    assertNotNull(this.factory.apply(0).toString());
+  }
+
+  /**
+   * Extract the result from a future or returns 'null' when an exception occurred
+   *
+   * @param future The future we want the result from
+   * @param <O>    The result type
+   * @return The result or 'null' when a checked exception occurred
+   */
+  private static <O> O get(Future<O> future) {
+    try {
+      return future.get();
+    } catch (InterruptedException | ExecutionException e) {
+      return null;
+    }
+  }
+
+}

thread-pool/src/test/java/com/iluwatar/threadpool/WorkerTest.java

@@ -0,0 +1,31 @@
+package com.iluwatar.threadpool;
+
+import org.junit.Test;
+
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.verifyNoMoreInteractions;
+import static org.mockito.Mockito.verifyZeroInteractions;
+
+/**
+ * Date: 12/30/15 - 18:21 PM
+ *
+ * @author Jeroen Meulemeester
+ */
+public class WorkerTest {
+
+  /**
+   * Verify if a worker does the actual job
+   */
+  @Test
+  public void testRun() {
+    final Task task = mock(Task.class);
+    final Worker worker = new Worker(task);
+    verifyZeroInteractions(task);
+
+    worker.run();
+    verify(task).getTimeMs();
+    verifyNoMoreInteractions(task);
+  }
+
+}