Add proper unit tests for composite pattern

composite/src/test/java/com/iluwatar/composite/MessengerTest.java

@@ -0,0 +1,90 @@
+package com.iluwatar.composite;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.io.ByteArrayOutputStream;
+import java.io.PrintStream;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+
+/**
+ * Date: 12/11/15 - 8:12 PM
+ *
+ * @author Jeroen Meulemeester
+ */
+public class MessengerTest {
+
+  /**
+   * The buffer used to capture every write to {@link System#out}
+   */
+  private ByteArrayOutputStream stdOutBuffer = new ByteArrayOutputStream();
+
+  /**
+   * Keep the original std-out so it can be restored after the test
+   */
+  private final PrintStream realStdOut = System.out;
+
+  /**
+   * Inject the mocked std-out {@link PrintStream} into the {@link System} class before each test
+   */
+  @Before
+  public void setUp() {
+    this.stdOutBuffer = new ByteArrayOutputStream();
+    System.setOut(new PrintStream(stdOutBuffer));
+  }
+
+  /**
+   * Removed the mocked std-out {@link PrintStream} again from the {@link System} class
+   */
+  @After
+  public void tearDown() {
+    System.setOut(realStdOut);
+  }
+
+  /**
+   * Test the message from the orcs
+   */
+  @Test
+  public void testMessageFromOrcs() {
+    final Messenger messenger = new Messenger();
+    testMessage(
+        messenger.messageFromOrcs(),
+        "Where there is a whip there is a way."
+    );
+  }
+
+  /**
+   * Test the message from the elves
+   */
+  @Test
+  public void testMessageFromElves() {
+    final Messenger messenger = new Messenger();
+    testMessage(
+        messenger.messageFromElves(),
+        "Much wind pours from your mouth."
+    );
+  }
+
+  /**
+   * Test if the given composed message matches the expected message
+   *
+   * @param composedMessage The composed message, received from the messenger
+   * @param message         The expected message
+   */
+  private void testMessage(final LetterComposite composedMessage, final String message) {
+    // Test is the composed message has the correct number of words
+    final String[] words = message.split(" ");
+    assertNotNull(composedMessage);
+    assertEquals(words.length, composedMessage.count());
+
+    // Print the message to the mocked stdOut ...
+    composedMessage.print();
+
+    // ... and verify if the message matches with the expected one
+    assertEquals(message, new String(this.stdOutBuffer.toByteArray()).trim());
+  }
+
+}