Add PowerMockito tests to verify System.exit() behaviour and mock objects.

Author: jdhoek

pom.xml

@@ -23,6 +23,24 @@
       <version>4.11</version>
       <scope>test</scope>
     </dependency>
+    <!--<dependency>-->
+      <!--<groupId>org.mockito</groupId>-->
+      <!--<artifactId>mockito-core</artifactId>-->
+      <!--<version>1.9.5</version>-->
+      <!--<scope>test</scope>-->
+    <!--</dependency>-->
+    <dependency>
+      <groupId>org.powermock</groupId>
+      <artifactId>powermock-module-junit4</artifactId>
+      <version>1.5.1</version>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.powermock</groupId>
+      <artifactId>powermock-api-mockito</artifactId>
+      <version>1.5.1</version>
+      <scope>test</scope>
+    </dependency>
     <dependency>
       <groupId>com.github.stefanbirkner</groupId>
       <artifactId>system-rules</artifactId>

src/main/java/com/example/hellowithtests/Hello.java

@@ -8,17 +8,19 @@
 public class Hello {
 
     static final String HELLO = "Hello!";
-    private short times;
+    public static final int MAXIMUM_AMOUNT_OF_TIMES = 20;
+    private short times = 1;
 
     /**
-     * Construct a new Hello instance.
+     * Set how many times "Hello!" should be said.
      *
      * @param times How many times should this class say "Hello!"? The value should be no larger than 20.
      * @throws IllegalArgumentException Thrown when times is larger than 20 or a negative number.
      */
-    public Hello(int times) {
-        if (times < 0 || times > 20) {
-            throw new IllegalArgumentException("Parameter «times» should be a positive integer no larger than 20.");
+    public void setTimes(int times) {
+        if (times < 0 || times > MAXIMUM_AMOUNT_OF_TIMES) {
+            throw new IllegalArgumentException("Parameter «times» should be a positive integer no larger than "
+                    + MAXIMUM_AMOUNT_OF_TIMES + ".");
         }
         this.times = (short) times;
     }

src/main/java/com/example/hellowithtests/HelloApp.java

@@ -29,9 +29,9 @@ public static void main(String[] args) {
             }
         }
 
-        Hello hi = null;
+        Hello hi = new Hello();
         try {
-            hi = new Hello(times);
+            hi.setTimes(times);
         } catch (IllegalArgumentException e) {
             System.err.println("Something went wrong: " + e.getMessage());
             System.exit(EXIT_STATUS_HELLO_FAILED);

src/test/java/com/example/hellowithtests/HelloAppTest.java

@@ -1,37 +1,60 @@
 package com.example.hellowithtests;
 
-import org.junit.Rule;
 import org.junit.Test;
-import org.junit.contrib.java.lang.system.ExpectedSystemExit;
+import org.junit.runner.RunWith;
+import org.powermock.api.mockito.PowerMockito;
+import org.powermock.core.classloader.annotations.PrepareForTest;
+import org.powermock.modules.junit4.PowerMockRunner;
+
+import static org.mockito.Mockito.*;
+import static org.powermock.api.mockito.PowerMockito.whenNew;
 
 /**
  * Unit test for HelloApp.
  * <p/>
  * A unit test aims to test all code and code paths of a specific class.
+ * <p/>
+ * This test uses PowerMock and Mockito to mock objects.
  */
+@RunWith(PowerMockRunner.class)
+@PrepareForTest({System.class, HelloApp.class})
 public class HelloAppTest {
 
-    @Rule
-    public final ExpectedSystemExit exit = ExpectedSystemExit.none();
-
     @Test
     public void testMain() {
         String[] args = {"1"};
         HelloApp.main(args);
     }
 
     @Test
-    public void testHelloError() {
-        exit.expectSystemExitWithStatus(HelloApp.EXIT_STATUS_HELLO_FAILED);
-        String[] args = {"21"};
+    public void testWrongArgument() {
+        PowerMockito.mockStatic(System.class);
+
+        String[] args = {"bicycle"};
         HelloApp.main(args);
+
+        // Did the program exit with the expected error code?
+        PowerMockito.verifyStatic(only());
+        System.exit(HelloApp.EXIT_STATUS_PARAMETER_NOT_UNDERSTOOD);
     }
 
     @Test
-    public void testWrongArgument() {
-        exit.expectSystemExitWithStatus(HelloApp.EXIT_STATUS_PARAMETER_NOT_UNDERSTOOD);
-        String[] args = {"bicycle"};
+    public void testHelloError() throws Exception {
+        PowerMockito.mockStatic(System.class);
+
+        // Mock Hello used by HelloApp to throw the expected exception when invoked with setTimes(5).
+        Hello hi = mock(Hello.class);
+        doThrow(new IllegalArgumentException("Nope.")).when(hi).setTimes(5);
+        // Sneakily insert our fake Hello class when it is created.
+        whenNew(Hello.class).withNoArguments().thenReturn(hi);
+
+        // We know this will raise the expected exception, because we mocked Hello.
+        String[] args = {"5"};
         HelloApp.main(args);
+
+        // Did the program exit with the expected error code?
+        PowerMockito.verifyStatic(only());
+        System.exit(HelloApp.EXIT_STATUS_HELLO_FAILED);
     }
 
     @Test

src/test/java/com/example/hellowithtests/HelloTest.java

@@ -21,7 +21,7 @@ public void testSayHello() {
         OutputStream os = new ByteArrayOutputStream();
         PrintStream stream = new PrintStream(os, true);
 
-        Hello hi = new Hello(1);
+        Hello hi = new Hello();
         hi.sayHello(stream);
 
         assertThat(os.toString(), is(equalTo(Hello.HELLO + "\n")));
@@ -32,7 +32,8 @@ public void testSayHelloAFewTimes() {
         OutputStream os = new ByteArrayOutputStream();
         PrintStream stream = new PrintStream(os, true);
 
-        Hello hi = new Hello(3);
+        Hello hi = new Hello();
+        hi.setTimes(3);
         hi.sayHello(stream);
 
         // Does it say "Hello!" three times?
@@ -42,11 +43,13 @@ public void testSayHelloAFewTimes() {
 
     @Test(expected = IllegalArgumentException.class)
     public void testIllegalArgumentForHello21() {
-        new Hello(21);
+        Hello hi = new Hello();
+        hi.setTimes(Hello.MAXIMUM_AMOUNT_OF_TIMES + 1);
     }
 
     @Test(expected = IllegalArgumentException.class)
     public void testIllegalArgumentForHelloNegative() {
-        new Hello(-1);
+        Hello hi = new Hello();
+        hi.setTimes(-1);
     }
 }