JUnit – Expected Exceptions Test

In JUnit, there are 3 ways to test the expected exceptions :

1. @Test, optional ‘expected’ attribute
2. Try-catch and always fail()
3. @Rule ExpectedException

P.S Tested with JUnit 4.12

1. @Test expected attribute

Use this if you only want to test the exception type, refer below :

package com.mkyong;

import org.junit.Test;
import java.util.ArrayList;

public class Exception1Test {

    @Test(expected = ArithmeticException.class)
    public void testDivisionWithException() {
        int i = 1 / 0;
    }

    @Test(expected = IndexOutOfBoundsException.class)
    public void testEmptyList() {
        new ArrayList<>().get(0);
    }

}

2. Try-catch and always fail()

This is a bit old school, widely used in JUnit 3. Test the exception type and also the exception detail. Refer below :

package com.mkyong;

import org.junit.Test;
import java.util.ArrayList;
import static junit.framework.TestCase.fail;
import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.MatcherAssert.assertThat;

public class Exception2Test {

    @Test
    public void testDivisionWithException() {
        try {
            int i = 1 / 0;
            fail(); //remember this line, else 'may' false positive
        } catch (ArithmeticException e) {
            assertThat(e.getMessage(), is("/ by zero"));
			//assert others
        }
    }

    @Test
    public void testEmptyList() {
        try {
            new ArrayList<>().get(0);
            fail();
        } catch (IndexOutOfBoundsException e) {
            assertThat(e.getMessage(), is("Index: 0, Size: 0"));
        }
    }


}

3. @Rule ExpectedException

This ExpectedException rule (since JUnit 4.7) let you test both the exception type and also the exception detail, same like “2. Try-catch and always fail()” method, but in a more elegant way :

package com.mkyong;

import com.mkyong.examples.CustomerService;
import com.mkyong.examples.exception.NameNotFoundException;
import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.ExpectedException;

import static org.hamcrest.CoreMatchers.containsString;
import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.Matchers.hasProperty;

public class Exception3Test {

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

    @Test
    public void testDivisionWithException() {

        thrown.expect(ArithmeticException.class);
        thrown.expectMessage(containsString("/ by zero"));

        int i = 1 / 0;

    }

    @Test
    public void testNameNotFoundException() throws NameNotFoundException {

		//test type
        thrown.expect(NameNotFoundException.class);

		//test message
        thrown.expectMessage(is("Name is empty!"));

        //test detail
        thrown.expect(hasProperty("errCode"));  //make sure getters n setters are defined.
        thrown.expect(hasProperty("errCode", is(666)));

        CustomerService cust = new CustomerService();
        cust.findByName("");

    }

}

package com.mkyong.examples.exception;

public class NameNotFoundException extends Exception {

    private int errCode;

    public NameNotFoundException(int errCode, String message) {
        super(message);
        this.errCode = errCode;
    }

    public int getErrCode() {
        return errCode;
    }

    public void setErrCode(int errCode) {
        this.errCode = errCode;
    }
}

package com.mkyong.examples;

import com.mkyong.examples.exception.NameNotFoundException;

public class CustomerService {

    public Customer findByName(String name) throws NameNotFoundException {

        if ("".equals(name)) {
            throw new NameNotFoundException(666, "Name is empty!");
        }

        return new Customer(name);

    }

}

References

1. JUnit Wiki Exception Testing
2. Java Custom Exception Examples