Added tests for singleton pattern

singleton/src/test/java/com/iluwatar/singleton/EnumIvoryTowerTest.java

@@ -0,0 +1,17 @@
+package com.iluwatar.singleton;
+
+/**
+ * Date: 12/29/15 - 19:20 PM
+ *
+ * @author Jeroen Meulemeester
+ */
+public class EnumIvoryTowerTest extends SingletonTest<EnumIvoryTower> {
+
+  /**
+   * Create a new singleton test instance using the given 'getInstance' method
+   */
+  public EnumIvoryTowerTest() {
+    super(() -> EnumIvoryTower.INSTANCE);
+  }
+
+}

singleton/src/test/java/com/iluwatar/singleton/InitializingOnDemandHolderIdiomTest.java

@@ -0,0 +1,17 @@
+package com.iluwatar.singleton;
+
+/**
+ * Date: 12/29/15 - 19:22 PM
+ *
+ * @author Jeroen Meulemeester
+ */
+public class InitializingOnDemandHolderIdiomTest extends SingletonTest<InitializingOnDemandHolderIdiom> {
+
+  /**
+   * Create a new singleton test instance using the given 'getInstance' method
+   */
+  public InitializingOnDemandHolderIdiomTest() {
+    super(InitializingOnDemandHolderIdiom::getInstance);
+  }
+
+}

singleton/src/test/java/com/iluwatar/singleton/IvoryTowerTest.java

@@ -0,0 +1,17 @@
+package com.iluwatar.singleton;
+
+/**
+ * Date: 12/29/15 - 19:23 PM
+ *
+ * @author Jeroen Meulemeester
+ */
+public class IvoryTowerTest extends SingletonTest<IvoryTower> {
+
+  /**
+   * Create a new singleton test instance using the given 'getInstance' method
+   */
+  public IvoryTowerTest() {
+    super(IvoryTower::getInstance);
+  }
+
+}

singleton/src/test/java/com/iluwatar/singleton/LazyLoadedSingletonThreadSafetyTest.java

@@ -1,90 +0,0 @@
-package com.iluwatar.singleton;
-
-import static org.junit.Assert.assertEquals;
-
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.List;
-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 org.junit.Test;
-
-/**
- * This class provides several test case that test singleton construction.
- *
- * The first proves that multiple calls to the singleton getInstance object are the same when called
- * in the SAME thread. The second proves that multiple calls to the singleton getInstance object are
- * the same when called in the DIFFERENT thread.
- *
- */
-public class LazyLoadedSingletonThreadSafetyTest {
-
-  private static final int NUM_THREADS = 5;
-  private List<ThreadSafeLazyLoadedIvoryTower> threadObjects = Collections
-      .synchronizedList(new ArrayList<>());
-
-  // NullObject class so Callable has to return something
-  private class NullObject {
-    private NullObject() {}
-  }
-
-  @Test
-  public void testMultipleCallsReturnTheSameObjectInSameThread() {
-    // Create several instances in the same calling thread
-    ThreadSafeLazyLoadedIvoryTower instance1 = ThreadSafeLazyLoadedIvoryTower.getInstance();
-    ThreadSafeLazyLoadedIvoryTower instance2 = ThreadSafeLazyLoadedIvoryTower.getInstance();
-    ThreadSafeLazyLoadedIvoryTower instance3 = ThreadSafeLazyLoadedIvoryTower.getInstance();
-    // now check they are equal
-    assertEquals(instance1, instance1);
-    assertEquals(instance1, instance2);
-    assertEquals(instance2, instance3);
-    assertEquals(instance1, instance3);
-  }
-
-  @Test
-  public void testMultipleCallsReturnTheSameObjectInDifferentThreads()
-      throws InterruptedException, ExecutionException {
-    {
-      // create several threads and inside each callable instantiate the singleton class
-      ExecutorService executorService = Executors.newSingleThreadExecutor();
-
-      List<Callable<NullObject>> threadList = new ArrayList<>();
-      for (int i = 0; i < NUM_THREADS; i++) {
-        threadList.add(new SingletonCreatingThread());
-      }
-
-      ExecutorService service = Executors.newCachedThreadPool();
-      List<Future<NullObject>> results = service.invokeAll(threadList);
-
-      // wait for all of the threads to complete
-      for (Future res : results) {
-        res.get();
-      }
-
-      // tidy up the executor
-      executorService.shutdown();
-    }
-    {
-      // now check the contents that were added to threadObjects by each thread
-      assertEquals(NUM_THREADS, threadObjects.size());
-      assertEquals(threadObjects.get(0), threadObjects.get(1));
-      assertEquals(threadObjects.get(1), threadObjects.get(2));
-      assertEquals(threadObjects.get(2), threadObjects.get(3));
-      assertEquals(threadObjects.get(3), threadObjects.get(4));
-    }
-  }
-
-  private class SingletonCreatingThread implements Callable<NullObject> {
-    @Override
-    public NullObject call() {
-      // instantiate the thread safety class and add to list to test afterwards
-      ThreadSafeLazyLoadedIvoryTower instance = ThreadSafeLazyLoadedIvoryTower.getInstance();
-      threadObjects.add(instance);
-      return new NullObject();// return null object (cannot return Void)
-    }
-  }
-}

singleton/src/test/java/com/iluwatar/singleton/SingletonTest.java

@@ -0,0 +1,88 @@
+package com.iluwatar.singleton;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.function.Supplier;
+
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertSame;
+
+/**
+ * This class provides several test case that test singleton construction.
+ *
+ * The first proves that multiple calls to the singleton getInstance object are the same when called
+ * in the SAME thread. The second proves that multiple calls to the singleton getInstance object are
+ * the same when called in the DIFFERENT thread.
+ *
+ * Date: 12/29/15 - 19:25 PM
+ *
+ * @author Jeroen Meulemeester
+ * @author Richard Jones
+ */
+public abstract class SingletonTest<S> {
+
+  /**
+   * The singleton's getInstance method
+   */
+  private final Supplier<S> singletonInstanceMethod;
+
+  /**
+   * Create a new singleton test instance using the given 'getInstance' method
+   *
+   * @param singletonInstanceMethod The singleton's getInstance method
+   */
+  public SingletonTest(final Supplier<S> singletonInstanceMethod) {
+    this.singletonInstanceMethod = singletonInstanceMethod;
+  }
+
+  /**
+   * Test the singleton in a non-concurrent setting
+   */
+  @Test
+  public void testMultipleCallsReturnTheSameObjectInSameThread() {
+    // Create several instances in the same calling thread
+    S instance1 = this.singletonInstanceMethod.get();
+    S instance2 = this.singletonInstanceMethod.get();
+    S instance3 = this.singletonInstanceMethod.get();
+    // now check they are equal
+    assertSame(instance1, instance2);
+    assertSame(instance1, instance3);
+    assertSame(instance2, instance3);
+  }
+
+  /**
+   * Test singleton instance in a concurrent setting
+   */
+  @Test(timeout = 10000)
+  public void testMultipleCallsReturnTheSameObjectInDifferentThreads() throws Exception {
+
+    // Create 10000 tasks and inside each callable instantiate the singleton class
+    final List<Callable<S>> tasks = new ArrayList<>();
+    for (int i = 0; i < 10000; i++) {
+      tasks.add(this.singletonInstanceMethod::get);
+    }
+
+    // Use up to 8 concurrent threads to handle the tasks
+    final ExecutorService executorService = Executors.newFixedThreadPool(8);
+    final List<Future<S>> results = executorService.invokeAll(tasks);
+
+    // wait for all of the threads to complete
+    final S expectedInstance = this.singletonInstanceMethod.get();
+    for (Future<S> res : results) {
+      final S instance = res.get();
+      assertNotNull(instance);
+      assertSame(expectedInstance, instance);
+    }
+
+    // tidy up the executor
+    executorService.shutdown();
+
+  }
+
+}

singleton/src/test/java/com/iluwatar/singleton/ThreadSafeDoubleCheckLockingTest.java

@@ -0,0 +1,17 @@
+package com.iluwatar.singleton;
+
+/**
+ * Date: 12/29/15 - 19:26 PM
+ *
+ * @author Jeroen Meulemeester
+ */
+public class ThreadSafeDoubleCheckLockingTest extends SingletonTest<ThreadSafeDoubleCheckLocking> {
+
+  /**
+   * Create a new singleton test instance using the given 'getInstance' method
+   */
+  public ThreadSafeDoubleCheckLockingTest() {
+    super(ThreadSafeDoubleCheckLocking::getInstance);
+  }
+
+}

singleton/src/test/java/com/iluwatar/singleton/ThreadSafeLazyLoadedIvoryTowerTest.java

@@ -0,0 +1,17 @@
+package com.iluwatar.singleton;
+
+/**
+ * Date: 12/29/15 - 19:26 PM
+ *
+ * @author Jeroen Meulemeester
+ */
+public class ThreadSafeLazyLoadedIvoryTowerTest extends SingletonTest<ThreadSafeLazyLoadedIvoryTower> {
+
+  /**
+   * Create a new singleton test instance using the given 'getInstance' method
+   */
+  public ThreadSafeLazyLoadedIvoryTowerTest() {
+    super(ThreadSafeLazyLoadedIvoryTower::getInstance);
+  }
+
+}