Spring Testing - Spring JUnit 4 Rules

Spring 4.12 introduced two JUnit rules: SpringClassRule and SpringMethodRule.

Instead of using @RunWith(SpringRunner.class), we can use these two rules to achieve the same result.

As JUnit framework allows only one Runner in a test class, Spring JUnit rules provide the flexibility to run tests in Spring context environment without using @RunWith(SpringRunner.class), which allows us to use other JUnit runners like Parameterized in the same test class.

Example

Creating a simple Spring application

@Component
@Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
public class ShoppingCart {
  private List<String> orders = new ArrayList<>();

  public void addItem(String name, int qty) {
      orders.add(String.format("order. Item:%s qty%s", name, qty));
  }

  public String checkout() {
      String msg = placeOrders();
      orders.clear();
      return msg;
  }

  public String placeOrders() {
      return orders.size() + " orders placed";
  }
}

@Configuration
@ComponentScan("com.logicbig.example")
public class AppConfig {
}

Writing JUnit test

@ContextConfiguration(classes = AppConfig.class)
public class ShoppingCartTest {

  @ClassRule
  public static final SpringClassRule SPRING_CLASS_RULE= new SpringClassRule();

  @Rule
  public final SpringMethodRule springMethodRule = new SpringMethodRule();

  @Autowired
  private ShoppingCart shoppingCart;

  @Test
  public void testCheckout() {
      shoppingCart.addItem("Item1", 3);
      shoppingCart.addItem("item2", 5);
      String result = shoppingCart.checkout();
      System.out.printf("Shopping cart checkout response: %s%n", result);
      Assert.assertEquals("2 orders placed", result);
  }
}

mvn -q test

Output

d:\example-projects\spring-core-testing\spring-junit-rules>mvn -q test

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running com.logicbig.example.ShoppingCartTest
Shopping cart checkout response: 2 orders placed
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.367 sec

Results :

Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

Note:

As seen in the above example, SpringMethodRule should always be annotated with @Rule and SpringClassRule should always be annotated with @ClassRule. That's because SpringMethodRule supports instance level features, whereas, SpringClassRule supports class level features.

Example Project

Dependencies and Technologies Used:

• spring-context 4.3.9.RELEASE: Spring Context.
• spring-test 4.3.9.RELEASE: Spring TestContext Framework.
• junit 4.12: JUnit is a unit testing framework for Java, created by Erich Gamma and Kent Beck.
• JDK 1.8
• Maven 3.3.9