Question

There is an interface:

interface IEventListener
{
  void onEvent(List <IEvent> events);
}

There is an event class:

class EventB
{
  private final int id;
  private final A a;
  private final String somethingElse;
...
// constructors, getters
...
}

And there is a class to test:

class Doer
{
 IEventListener eventListener;
 void doSomething(Aaa a)
 {
   eventListener.onEvent(Arrays.asList(new EventA(1), new EventC(2)));
...
   eventListener.onEvent(Arrays.asList(new EventB(42, a.getA(), "foo"), new EventA(3), new EventB(0, a.getA(), "bar")));
...
   eventListener.onEvent(Arrays.asList(new EventC(4)));
 }
}

The Doer is a code which I need to test, the method doSomething produces packs of events, and I need to test if it produces a particular event in some specific conditions.

More precisely I want to have a unit test which calls the method doSomething and checks that EventB is sent with “42” and A as from method argument a. All other events should be ignored.

To make such test I’ve only came up with solution involving quite verbose code with ArgumentCaptor, for-blocks, and magic boolean flags…

What is the best way to make a unit test for it? Maybe the code design is bad?

Answer 1

The design is correct, this is how you test it with Mockito:

import org.hamcrest.Matchers;
import org.mockito.Mockito;
public void firesEventsOnDoSomething() {
  Listener listener = Mockito.mock(Listener.class);
  Doer doer = new Doer(listener);
  doer.doSomething(aaa);
  Mockito.verify(listener).onEvent(
    Mockito.argThat(
      Matchers.hasItem(
        Matchers.allOf(
          Matchers.instanceOf(EventB.class),
          Matchers.hasProperty("a", Matchers.equalTo(aaa.getA())),
          // whatever you want
        )
      )
    )
  );
}

It’s Mockito 1.9.0 and Hamcrest-library 1.2.1.

To use JUnit 4.10 together with Hamcrest-library 1.2.1 you should use junit:junit-dep:4.10 artifact, and exclude org.hamcrest:hamcrest-core from it:

<dependency>
  <groupId>junit</groupId>
  <artifactId>junit-dep</artifactId>
  <version>4.10</version>
  <scope>test</scope>
  <exclusions>
    <exclusion>
      <groupId>org.hamcrest</groupId>
      <artifactId>hamcrest-core</artifactId>
    </exclusion>
  </exclusions>
</dependency>
<dependency>
  <groupId>org.hamcrest</groupId>
  <artifactId>hamcrest-core</artifactId>
  <version>1.2.1</version>
  <scope>test</scope>
</dependency>
<dependency>
  <groupId>org.hamcrest</groupId>
  <artifactId>hamcrest-library</artifactId>
  <version>1.2.1</version>
  <scope>test</scope>
</dependency>
<dependency>
  <groupId>org.mockito</groupId>
  <artifactId>mockito-core</artifactId>
  <version>1.9.0</version>
  <scope>test</scope>
  <exclusions>
    <exclusion>
      <groupId>org.hamcrest</groupId>
      <artifactId>hamcrest-core</artifactId>
    </exclusion>
  </exclusions>
</dependency>