AssertJ 3.0.0 release for Java 8 makes testing exceptions much easier than before. In one of my previous blog post I described how to utilize plain Java 8 to achieve this, but with AssertJ 3.0.0 much of the code I created may be removed.
Warning: this blog post contains mostly the code examples.
SUT – System Under Test
We will test exceptions thrown by the below 2 classes.
The first one:
class DummyService {
public void someMethod() {
throw new RuntimeException("Runtime exception occurred");
}
public void someOtherMethod(boolean b) {
throw new RuntimeException("Runtime exception occurred",
new IllegalStateException("Illegal state"));
}
}And the second:
class DummyService2 {
public DummyService2() throws Exception {
throw new Exception("Constructor exception occurred");
}
public DummyService2(boolean dummyParam) throws Exception {
throw new Exception("Constructor exception occurred");
}
}assertThatThrownBy() examples
Note: static import of org.assertj.core.api.Assertions.assertThatThrownBy is required in order to make the below code work properly.
@Test
public void verifiesTypeAndMessage() {
assertThatThrownBy(new DummyService()::someMethod)
.isInstanceOf(RuntimeException.class)
.hasMessage("Runtime exception occurred")
.hasNoCause();
}
@Test
public void verifiesCauseType() {
assertThatThrownBy(() -> new DummyService().someOtherMethod(true))
.isInstanceOf(RuntimeException.class)
.hasMessage("Runtime exception occurred")
.hasCauseInstanceOf(IllegalStateException.class);
}
@Test
public void verifiesCheckedExceptionThrownByDefaultConstructor() {
assertThatThrownBy(DummyService2::new)
.isInstanceOf(Exception.class)
.hasMessage("Constructor exception occurred");
}
@Test
public void verifiesCheckedExceptionThrownConstructor() {
assertThatThrownBy(() -> new DummyService2(true))
.isInstanceOf(Exception.class)
.hasMessage("Constructor exception occurred");
}The assertions presented comes from AbstractThrowableAssert and there are much more of them for you to use!
No exception thrown!
The below test will fail as no exception is thrown:
@Test
public void failsWhenNoExceptionIsThrown() {
assertThatThrownBy(() -> System.out.println());
}The message is:
java.lang.AssertionError: Expecting code to raise a throwable.
AAA Style
If you wish to distinguish act and assert phases of the test for improving readability, it is also possible:
@Test
public void aaaStyle() {
// arrange
DummyService dummyService = new DummyService();
// act
Throwable throwable = catchThrowable(dummyService::someMethod);
// assert
assertThat(throwable)
.isNotNull()
.hasMessage("Runtime exception occurred");
}References
- Source code for this article is available on GitHub (have a look at
com.github.kolorobot.assertj.exceptionspackage) - AssertJ 3.0.0 for Java 8 release
| Reference: | JUnit: Testing Exceptions with Java 8 and AssertJ 3.0.0 from our JCG partner Rafal Borowiec at the Codeleak.pl blog. |
