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