Add proper unit tests for double-dispatch pattern

double-dispatch/src/test/java/com/iluwatar/doubledispatch/CollisionTest.java

@@ -0,0 +1,136 @@
+package com.iluwatar.doubledispatch;
+
+import org.junit.After;
+import org.junit.Before;
+
+import java.io.PrintStream;
+import java.util.Objects;
+
+import static org.junit.Assert.assertEquals;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.verifyNoMoreInteractions;
+
+/**
+ * Date: 12/10/15 - 8:37 PM
+ *
+ * @author Jeroen Meulemeester
+ */
+public abstract class CollisionTest<O extends GameObject> {
+
+  /**
+   * The mocked standard out {@link PrintStream}, required if some of the actions on the tested
+   * object don't have a direct influence on any other accessible objects, except for writing to
+   * std-out using {@link System#out}
+   */
+  private final PrintStream stdOutMock = mock(PrintStream.class);
+
+  /**
+   * Keep the original std-out so it can be restored after the test
+   */
+  private final PrintStream stdOutOrig = System.out;
+
+  /**
+   * Inject the mocked std-out {@link PrintStream} into the {@link System} class before each test
+   */
+  @Before
+  public void setUp() {
+    System.setOut(this.stdOutMock);
+  }
+
+  /**
+   * Removed the mocked std-out {@link PrintStream} again from the {@link System} class
+   */
+  @After
+  public void tearDown() {
+    System.setOut(this.stdOutOrig);
+  }
+
+  /**
+   * Get the mocked stdOut {@link PrintStream}
+   *
+   * @return The stdOut print stream mock, renewed before each test
+   */
+  final PrintStream getStdOutMock() {
+    return this.stdOutMock;
+  }
+
+  /**
+   * Get the tested object
+   *
+   * @return The tested object, should never return 'null'
+   */
+  abstract O getTestedObject();
+
+  /**
+   * Collide the tested item with the other given item and verify if the damage and fire state is as
+   * expected
+   *
+   * @param other        The other object we have to collide with
+   * @param otherDamaged Indicates if the other object should be damaged after the collision
+   * @param otherOnFire  Indicates if the other object should be burning after the collision
+   * @param thisDamaged  Indicates if the test object should be damaged after the collision
+   * @param thisOnFire   Indicates if the other object should be burning after the collision
+   * @param description  The expected description of the collision
+   */
+  void testCollision(final GameObject other, final boolean otherDamaged, final boolean otherOnFire,
+                     final boolean thisDamaged, final boolean thisOnFire, final String description) {
+
+    Objects.requireNonNull(other);
+    Objects.requireNonNull(getTestedObject());
+
+    final O tested = getTestedObject();
+
+    tested.collision(other);
+
+    verify(getStdOutMock(), times(1)).println(description);
+    verifyNoMoreInteractions(getStdOutMock());
+
+    testOnFire(other, tested, otherOnFire);
+    testDamaged(other, tested, otherDamaged);
+
+    testOnFire(tested, other, thisOnFire);
+    testDamaged(tested, other, thisDamaged);
+
+  }
+
+  /**
+   * Test if the fire state of the target matches the expected state after colliding with the given
+   * object
+   *
+   * @param target             The target object
+   * @param other              The other object
+   * @param expectTargetOnFire The expected state of fire on the target object
+   */
+  private void testOnFire(final GameObject target, final GameObject other, final boolean expectTargetOnFire) {
+    final String targetName = target.getClass().getSimpleName();
+    final String otherName = other.getClass().getSimpleName();
+
+    final String errorMessage = expectTargetOnFire ?
+        "Expected [" + targetName + "] to be on fire after colliding with [" + otherName + "] but it was not!" :
+        "Expected [" + targetName + "] not to be on fire after colliding with [" + otherName + "] but it was!";
+
+    assertEquals(errorMessage, expectTargetOnFire, target.isOnFire());
+  }
+
+  /**
+   * Test if the damage state of the target matches the expected state after colliding with the
+   * given object
+   *
+   * @param target         The target object
+   * @param other          The other object
+   * @param expectedDamage The expected state of damage on the target object
+   */
+  private void testDamaged(final GameObject target, final GameObject other, final boolean expectedDamage) {
+    final String targetName = target.getClass().getSimpleName();
+    final String otherName = other.getClass().getSimpleName();
+
+    final String errorMessage = expectedDamage ?
+        "Expected [" + targetName + "] to be damaged after colliding with [" + otherName + "] but it was not!" :
+        "Expected [" + targetName + "] not to be damaged after colliding with [" + otherName + "] but it was!";
+
+    assertEquals(errorMessage, expectedDamage, target.isDamaged());
+  }
+
+}