check errorcode with @rule in junit

Question

I found @Rule annotation in jUnit for better handling of exception. Is there a way to check error code ?

Currently my code looks like (without @Rule):

 @Test
    public void checkNullObject() {
    MyClass myClass= null;
    try {
        MyCustomClass.get(null); // it throws custom exception when null is passed
    } catch (CustomException e) { // error code is error.reason.null
        Assert.assertSame("error.reason.null", e.getInformationCode());
    }
    }

But with use of @Rule, I am doing following :

        @Rule
        public ExpectedException exception = ExpectedException.none();

        @Test
        public void checkNullObject() throws CustomException {
        exception.expect(CustomException .class);
        exception.expectMessage("Input object is null.");
        MyClass myClass= null;
        MyCustomClass.get(null);

        }

But, I want to do something like below:

       @Rule
        public ExpectedException exception = ExpectedException.none();

        @Test
        public void checkNullObject() throws CustomException {
        exception.expect(CustomException .class);
       //currently below line is not legal. But I need to check errorcode.
        exception.errorCode("error.reason.null");
        MyClass myClass= null;
        MyCustomClass.get(null);

        }

Answer 1

You can use a custom matcher on the rule with the expect(Matcher<?> matcher) method.

For example:

public class ErrorCodeMatcher extends BaseMatcher<CustomException> {
  private final String expectedCode;

  public ErrorCodeMatcher(String expectedCode) {
    this.expectedCode = expectedCode;
  }

  @Override
  public boolean matches(Object item) {
    CustomException e = (CustomException)item;
    return expectedCode.equals(e.getInformationCode());
  }
}

and in the test:

exception.expect(new ErrorCodeMatcher("error.reason.null"));