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About Rafal Borowiec

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Yet another way to handle exceptions in JUnit: catch-exception

There are many ways of handling exceptions in JUnit (3 ways of handling exceptions in JUnit. Which one to choose?, JUnit ExpectedException rule: beyond basics). In this post I will introduce catch-exception library that I was recommended to give a try. In short, catch-exceptions is a library that catches exceptions in a single line of code and makes them available for further analysis.

Install via Maven

In order to get started quickly, I used my Unit Testing Demo project with a set of test dependencies (JUnit, Mocito, Hamcrest, AssertJ) and added catch-exceptions:


So the dependency tree looks as follows:

[INFO] --- maven-dependency-plugin:2.1:tree @ unit-testing-demo ---
[INFO] com.github.kolorobot:unit-testing-demo:jar:1.0.0-SNAPSHOT
[INFO] +- org.slf4j:slf4j-api:jar:1.5.10:compile
[INFO] +- org.slf4j:jcl-over-slf4j:jar:1.5.10:runtime
[INFO] +- org.slf4j:slf4j-log4j12:jar:1.5.10:runtime
[INFO] +- log4j:log4j:jar:1.2.15:runtime
[INFO] +- junit:junit:jar:4.11:test
[INFO] +- org.mockito:mockito-core:jar:1.9.5:test
[INFO] +- org.assertj:assertj-core:jar:1.5.0:test
[INFO] +- org.hamcrest:hamcrest-core:jar:1.3:test
[INFO] +- org.hamcrest:hamcrest-library:jar:1.3:test
[INFO] +- org.objenesis:objenesis:jar:1.3:test
[INFO] \- com.googlecode.catch-exception:catch-exception:jar:1.2.0:test

Getting started

System under test (SUT):

class ExceptionThrower {
    void someMethod() {
        throw new RuntimeException("Runtime exception occurred");
    void someOtherMethod() {
        throw new RuntimeException("Runtime exception occurred",
                new IllegalStateException("Illegal state"));
    void yetAnotherMethod(int code) {
        throw new CustomException(code);

The basic catch-exception BDD-style approach example with AssertJ assertions:

import org.junit.Test;
import static com.googlecode.catchexception.CatchException.*;
import static com.googlecode.catchexception.apis.CatchExceptionAssertJ.*;
public class CatchExceptionsTest {
    public void verifiesTypeAndMessage() {
        when(new SomeClass()).someMethod();
                .hasMessage("Runtime exception occurred")

Looks good. Concise, readable. No JUnit runners. Please note, that I specified which method of SomeClass I expect to throw an exception. As you can imagine, I can check multiple exceptions in one test. Although I would not recommend this approach as it may feel like violating a single responsibility of a test.

By the way, if you are working with Eclipse this may be handy for you: Improve content assist for types with static members while creating JUnit tests in Eclipse

Verify the cause

I think there is no comment needed for the below code:

import org.junit.Test;
import static com.googlecode.catchexception.CatchException.*;
import static com.googlecode.catchexception.apis.CatchExceptionAssertJ.*;
public class CatchExceptionsTest {
    public void verifiesCauseType() {
        when(new ExceptionThrower()).someOtherMethod();
                .hasMessage("Runtime exception occurred")

Verify custom exception with Hamcrest

To verify a custom exception I used the Hamcrest matcher code from my previous post:

class CustomException extends RuntimeException {
    private final int code;
    public CustomException(int code) {
        this.code = code;
    public int getCode() {
        return code;
class ExceptionCodeMatches extends TypeSafeMatcher<CustomException> {
    private int expectedCode;
    public ExceptionCodeMatches(int expectedCode) {
        this.expectedCode = expectedCode;
    protected boolean matchesSafely(CustomException item) {
        return item.getCode() == expectedCode;
    public void describeTo(Description description) {
        description.appendText("expects code ")
    protected void describeMismatchSafely(CustomException item, Description mismatchDescription) {
        mismatchDescription.appendText("was ")

And the test:

import org.junit.Test;
import static com.googlecode.catchexception.CatchException.*;
import static org.junit.Assert.*;
public class CatchExceptionsTest {
    public void verifiesCustomException() {
        catchException(new ExceptionThrower(), CustomException.class).yetAnotherMethod(500);
        assertThat((CustomException) caughtException(), new ExceptionCodeMatcher(500));


catch-exception looks really good. It is easy to get started quickly. I see some advantages over method rule in JUnit. If I have a chance, I will investigate the library more thoroughly, hopefully in a real-world project.

In case you are interested, please have a look at my other posts:

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