Mockobor

Mocked Observable Observation - a java library to simulate sending of events (via java listeners) from a mocked collaborator to a tested object.

When writing a lot of unit tests for large Java enterprise applications, certain problems tend to occur repeatedly:

Simulating the sending of events (via Java listeners) from mocked collaborators to tested objects.
Verifying the complete deregistration of listeners registered by mocked collaborators.

And all of these needs to be done without modifying production code.

While this process can be done manually, Mockobor makes it simpler, faster, and requires fewer implementation details in your tests.

Dependencies
Examples
Detailed Usage
Extensions
- Defining a Custom Listener Detector
- Using unsupported mocking tools
Restrictions
Installation
Changelog
Contributing

Dependencies

Mockobor depends only on the following libraries:

eclipse non-null annotations (org.eclipse.jdt.annotation)

To use Mockobor in unit tests:

Ensure you are using Java 11 or more recent version.
Include at least one of the following mocking tools in your tests:
- Mockito 5.0.0+
- EasyMock 3.4+
- Other mocking tools can also be added — refer to Using unsupported mocking tools.

if you use java 8 or Mockito 2.20.1 - 4.11.0, you can still use Mockobor 1.0.5 (Maven Central)

Examples

simulate the sending of events from a mocked collaborator to the tested object

Given that you have the following classes in your Java application:

Your class under test, which adds (for example, in the constructor) a listener to a specified observable object and removes it in another method (for example, in destroy()):

/** Object that you want to test. */
public class TestedObserver {

	private final SomeObservable         someObservable;
	private final Observer               observer               = new ObserverIml();
	private final PropertyChangeListener propertyChangeListener = new PropertyChangeListenerImpl();
	private final MyListener             myListener             = new MyListenerImpl();
	private final MyAnotherListener      myAnotherListener      = new MyAnotherListenerImpl();

	/** It registers some listeners by the specified (in tests - mocked) observable object. */
	public TestedObserver( SomeObservable someObservable ) {
		this.someObservable = someObservable;
		someObservable.addPropertyChangeListener( "prop", propertyChangeListener );
		someObservable.addMyListener( "sel", myListener );
		someObservable.addTwoListeners( myListener, myAnotherListener );
		someObservable.addObserver( observer );
	}

	/** And removes all listeners on destroy. */
	public void destroy() {
		someObservable.deleteObserver( observer );
		someObservable.removeTwoListeners( myListener, myAnotherListener );
		someObservable.removeMyListener( "sel", myListener );
		someObservable.removePropertyChangeListener( "prop", propertyChangeListener );
	}
}

Note: It is not strictly necessary to register listeners by directly invoking addXxxListener methods. Registration can be performed using annotations, aspects, or other mechanisms. What is important is that the registration methods of the observable object are invoked somewhere.

A collaborator of the tested object that fires events to the registered listeners:

/** Some observable object with ability to register listeners/observers. */
public interface SomeObservable {

	// property change support
	void addPropertyChangeListener( String propertyName, PropertyChangeListener listener );
	void removePropertyChangeListener( String propertyName, PropertyChangeListener listener );

	// typical java listeners
	void addMyListener( String selector, MyListener myAnotherListener );
	void removeMyListener( String selector, MyListener myAnotherListener );

	// another typical java listeners
	void addTwoListeners( MyListener myListener, MyAnotherListener myAnotherListener );
	void removeTwoListeners( MyListener myListener, MyAnotherListener myAnotherListener );

	// Observable
	void addObserver( Observer o );
	void deleteObserver( Observer o );
}

and listeners:

public interface MyListener {
	void somethingChanged1( Object somethingNewValue );
	int somethingChanged2( Object somethingNewValue );
}

public interface MyAnotherListener {
	void somethingOtherChanged( Object somethingOtherValue );
}

In tests, we mock the collaborator (SomeObservable) using one of the supported mocking tools (see Dependencies) and create a notifier object (ListenersNotifier) to send events:

class TestedObserver_Test {
	// create mock of SomeObservable 
	private final SomeObservable mockedObservable = Mockito.mock( SomeObservable.class );

	// create notifier for SomeObservable
	private final ListenersNotifier notifier = Mockobor.createNotifierFor( mockedObservable );

	// Object under tested. It registers listeners by the specified SomeObservable object.
	private final TestedObserver testObject = new TestedObserver( mockedObservable );
  
  ...
}

typical java style listeners

As you can see, SomeObservable uses (among other things) typical Java-style listeners, such as MyListener, with registration methods like addMyListener and removeMyListener. Mockobor treats such classes as "using a typical Java listener" and creates a base notifier—ListenersNotifier—to send events.

Now, to simulate processes in SomeObservable, we will send events to the listeners MyListener and MyAnotherListener, which are registered in the constructor of TestedObserver:

class TestedObserver_Test {
	private final SomeObservable    mockedObservable = Mockito.mock( SomeObservable.class );
	private final ListenersNotifier notifier         = Mockobor.createNotifierFor( mockedObservable );
	private final TestedObserver    testObject       = new TestedObserver( mockedObservable );

	@Test
	void testSendEventToJavaStyleListeners() {
		// Send events to testObject using listener interfaces (first method):
		( (MyListener) notifier ).somethingChanged1( newValue );
		int answer1 = ( (MyListener) notifier ).somethingChanged2( newValue2 );
		( (MyAnotherListener) notifier ).somethingOtherChanged( newValue3 );

		// Send events to testObject using ListenersNotifier (another approach, identical to the above):
		notifier.notifierFor( MyListener.class ).somethingChanged1( newValue );
		int answer2 = notifier.notifierFor( MyListener.class ).somethingChanged2( newValue2 );
		notifier.notifierFor( MyAnotherListener.class ).somethingOtherChanged( newValue3 );

		// If listeners are registered with a specific non-empty qualifier  
		// (e.g., in the `TestedObserver` constructor: someObservable.addMyListener("sel", myListener)),
		// you can then send events to those listeners:
		notifier.notifierFor( "sel", MyListener.class ).somethingChanged1( newValue );
		notifier.notifierFor( MyListener.class, selector( "sel" ) ).somethingChanged1( newValue ); // exactly as above

		// To notify (send the same event to) listeners of the same class 
		// that are registered with at least one of the specified selectors 
		// (in this case: either without a selector or with "sel" as the selector):
		notifier.notifierFor( MyListener.class, selector(), selector( "sel" ) ).somethingChanged1( newValue );
	}
}

See also UsageExample_TypicalJavaListener_Test.java

PropertyChangeListener

If your collaborator (observable object) provides methods such as
void addPropertyChangeListener(PropertyChangeListener listener) or
void addPropertyChangeListener(String propertyName, PropertyChangeListener listener),
it is treated as "similar to PropertyChangeSupport." In such cases, Mockobor creates a specialized notifier called PropertyChangeNotifier:

class TestedObserver_Test {
	private final SomeObservable    mockedObservable = Mockito.mock( SomeObservable.class );
	private final ListenersNotifier notifier         = Mockobor.createNotifierFor( mockedObservable );
	private final TestedObserver    testObject       = new TestedObserver( mockedObservable );

	@Test
	void testSendEventToPropertyChangeListeners() {
		// using PropertyChangeNotifier
		PropertyChangeNotifier propertyChangeNotifier = (PropertyChangeNotifier) notifier;
		propertyChangeNotifier.firePropertyChange( null, "o2", "n2" );
		propertyChangeNotifier.firePropertyChange( "prop", "o1", "n1" );

		// using ListenersNotifier
		notifier.notifierFor( PropertyChangeListener.class )
		        .propertyChange( new PropertyChangeEvent( mockedObservable, "p4", "o4", "n4" ) );


		// Using `ListenersNotifier` with selectors  
		// behaves exactly the same as:  
		// - `propertyChangeNotifier.firePropertyChange(null, 'o5', 'n5')`  
		// - `propertyChangeNotifier.firePropertyChange('prop', 'o5', 'n5')`    
		notifier.notifierFor( PropertyChangeListener.class, selector(), selector( "prop" ) )
		        .propertyChange( new PropertyChangeEvent( mockedObservable, "prop", "o5", "n5" ) );

		// direct using listener interface (PropertyChangeListener) 
		( (PropertyChangeListener) notifier )
				.propertyChange( new PropertyChangeEvent( mockedObservable, "prop", "o3", "n3" ) );
	}
}

See also UsageExample_BeanPropertyChange_Test.java

Observable, Observer

If your collaborator (observable object) provides a method such as void addObserver(Observer observer), it is treated as "similar to Observable." In such cases, Mockobor creates a specialized notifier called ObservableNotifier:

class TestedObserver_Test {
	private final SomeObservable    mockedObservable = Mockito.mock( SomeObservable.class );
	private final ListenersNotifier notifier         = Mockobor.createNotifierFor( mockedObservable );
	private final TestedObserver    testObject       = new TestedObserver( mockedObservable );

	@Test
	void testSendEventToPropertyChangeListeners() {
		// using ObservableNotifier
		ObservableNotifier observableNotifier = (ObservableNotifier) notifier;
		observableNotifier.notifyObservers();
		observableNotifier.notifyObservers( "v1" );

		// using ListenersNotifier
		notifier.notifierFor( Observer.class ).update( null, "v3" );

		// direct using listener interface (Observer)
		( (Observer) notifier ).update( null, "v2" );
	}
}

See also UsageExample_Observable_Test.java

ensure complete deregistration of listeners

You can use Mockobor to verify whether all listeners registered by the mocked observable object have been unregistered:

class TestedObserver_Test {
	private final SomeObservable    mockedObservable = Mockito.mock( SomeObservable.class );
	private final ListenersNotifier notifier         = Mockobor.createNotifierFor( mockedObservable );
	private final TestedObserver    testObject       = new TestedObserver( mockedObservable );

	@Test
	void testAllListenersAreRemoved() {

		// tested object should remove itself from the specified PropertyChangeSupport object on close.
		testObject.destroy(); // or close() or dispose() etc.

		// check that all listeners are unregistered
		Mockobor.assertThatAllListenersAreUnregistered( notifier );
	}
}

See also UsageExample_allListenersAreUnregistered_Test.java

use Mockito annotations and Mockobor together

If you are using Mockito as your mocking tool, you can seamlessly combine Mockito annotations with Mockobor:

@Mock
private SomeObservable mockedObservable;

@InjectMocks
private AnnotationsTestObject testedObserver;

private ListenersNotifier notifier;

@Test
void test_notifications() {
  ...
	notifie = Mockobor.createNotifierFor( mockedObservable );
  ...
	notifier.notifierFor( MyListener.class ).onChange( 1f );
  ...
}

See UsageExample_MockitoAnnotation_Test.java

Detailed Usage

monitor a mocked observable object and verify the complete deregistration of its listeners

To simulate event sending (via Java listeners) from a mocked collaborator to the tested object, Mockobor generates a special notifier object for the mocked observable:

ListenersNotifier notifier = Mockobor.createNotifierFor( mockedObservableObject )

Note: Your test object must listen to the same instance of the mocked observable object specified in the Mockobor.createNotifierFor invocation.

The notifier object implements the following interfaces, depending on the methods found in the specified mocked observable object:

ListenerNotifier – always implements.
XxxListener (standard Java-style listener) – implements if methods like addXxxListener(XxxListener) are detected.
PropertyChangeNotifier + PropertyChangeListener – implements if methods like addPropertyChangeListener(PropertyChangeListener) are detected.
ObservableNotifier + Observer – implements if methods like addObserver(Observer) are detected.

This notifier object can be utilized to perform the following actions:

Send events to the test object:
- Using the notifierFor method: notifier.notifierFor(XxxListener.class).<listener method>(arguments)
- Directly via the listener interface: ((XxxListener) notifier).<listener method>(arguments)
- Using PropertyChangeNotifier (when applicable): ((PropertyChangeNotifier) notifier).firePropertyChange(...)
- Using ObservableNotifier (when applicable): ((ObservableNotifier) notifier).notifyObservers(...)
Verify complete deregistration of listeners:
- For a single notifier:
  assertThat(notifier.allListenersAreUnregistered()).isTrue()
- For multiple notifiers:
  Mockobor.assertThatAllListenersAreUnregistered(notifier1, ..., notifierN)

For more details see JavaDoc (Mockobor, Mockobor.createNotifierFor , Mockobor.assertThatAllListenersAreUnregistered, ListenerNotifier) and Examples.

listener selectors

Sometimes, a listener should or can be registered not for all events, but only for specific qualified events. For example, in java.beans.PropertyChangeSupport.addPropertyChangeListener(String propertyName, PropertyChangeListener listener), the propertyName serves as a qualifier. In such cases, Mockobor utilizes a selector. It identifies 'selector' arguments in registration methods and allows the addition of selectors when sending notifications:

// In production code, the object under test registers its listener
public class ClassUnderTest {
  ...

	void someInitMethod() {
    ...
		observable.addMyListener( "q1", "q2", listner1 );  // ("q1", "q2") is the selector here
		observable.addMyListener( "q3", listener2 ); // "q3" is the selector here
		observable.addMyListener( listener3 ); // the selector is empty here
    ...
	}
 ...
}

// In tests, send notifications to the listeners in the object under test.
class SomeTest {
  ...

	@Test
	void someTestMethod() {
    ...
		// Send a notification to the listener registered with the selector ('q1', 'q2'):
		notifier.notiferFor( listner1.class, selector( "q1", "q2" ) ).listener_method();

		// Send a notification to the listener registered with the selector "q3":
		notifier.notiferFor( "q3", listner2.class ).listener_method();
		notifier.notifierFor( listener2.class, selector( "q3" ) ).listener_method(); // identical to the line above

		// Send a notifications to the listener registered without a selector or with an empty selector: 
		notifier.notiferFor( listner3.class ).listener_method();
		notifier.notifierFor( listener3.class, selector() ).listener_method();  // identical to the line above

		// Send a notifications to the listeners registered with any of the specified selectors
		// (here, all three: listener1, listener2 and listener3; see "someInitMethod" above)
		notifier.notiferFor( listner1.class, selector( "q1", "q2" ), selector( "q3" ), selector() ).listener_method();
    ...
	}
  ...
}

For more details see Examples / typical java style listeners

registration order

Typically, the listener notifier object is created prior to the tested object registering its listeners via the mocked observable. This method is reliable and compatible with all mocking tools:

class SomeTest {
	private final SomeObservable    mockedObservable = EasyMock.mock( SomeObservable.class );
	private final ListenersNotifier notifier         = Mockobor.createNotifierFor( mockedObservable );  // (1) the listener notifier created
	private final TestedObserver    testObject       = new TestedObserver( mockedObservable ); // (2) the tested object registers its listeners
  ...
}

Alternatively, if you are using Mockito, you have the flexibility to create a listener notifier object whenever needed:

class SomeTest {
	private final SomeObservable mockedObservable = Mockito.mock( SomeObservable.class );
	private final TestedObserver testObject       = new TestedObserver( mockedObservable );

	@Test
	void test_notifications() {
    ...
		notifie = ockobor.createNotifierFor( mockedObservable );
    ...
		notifier.notifierFor( XxxListener.class ).onChange(...);
    ...
	}
}

It allows usage of Mockito annotations together with Mockobor. See Examples / use Mockito annotations and Mockobor together

Note: This is not compatible with EasyMock! See Restrictions / EasyMock restrictions

listener notifier settings

NotifierSettings can be used to control the following aspects of the creation and behavior of a listener notifier:

Strict or lenient checking to determine if the list of listeners selected for sending notifications contains any listeners:
- strict (default) - Throws a ListenersNotFoundException if no listener is selected to receive the notification.
- lenient - Does nothing if no listener is selected.
Interface implementation by a new listener notifier:
- true (default) - All new ListenersNotifier instances returned from Mockobor.createNotifierFor implement all detected listener interfaces. This allows events to be fired using either of the following approaches:
  - ((MyListener) notifier).somethingChanged(...)
  - notifier.notifierFor(MyListener.class).somethingChanged(...)
- false - New ListenersNotifier instances do not implement listener interfaces. As a result, events can only be fired using the following approach:
  - notifier.notifierFor(MyListener.class).somethingChanged(...)

NotifierSettings can be changed globally for all future ListenersNotifier instances by modifying the settings stored statically in MockoborContext:

  MockoborContext.updateNotifierSettings().

ignoreListenerInterfaces().

lenientListenerListCheck();

or exclusively for one-time use during creation:

  ListenersNotifier notifier = Mockobor.createNotifierFor(
		mockedObservable,
		Mockobor.notifierSettings().ignoreListenerInterfaces().lenientListenerListCheck();

For more details see UsageExample_NotifierSettings_Test.java

Extensions

Defining a Custom Listener Detector

Out of the box Mockobor supports three kinds of listeners:

Typical Java-style listeners, where listener class names follow the pattern XxxListener, and registration method names follow conventions like addXxxListener and removeXxxListener (see Typical Java-style Listeners Example).
java.beans.PropertyChangeListener, considered a subclass of typical Java-style listeners ( see PropertyChangeListener Example).
java.util.Observable / java.util.Observer (see Observable / Observer Example).

If you have a different type of listener, you can add support for it by following these steps:

Create a custom implementation of ListenerDefinitionDetector.
Register it using the method MockoborContext.registerListenerDefinitionDetector(yourListenerDetector).

To implement ListenerDefinitionDetector, you typically need to extend AbstractDetector and implement/override the following methods:

isListenerClass(Class, Method): Verifies if the specified parameter type is a listener type.
isAddMethods(Method): Determines if the specified method is a listener registration method (for adding listeners).
isRemoveMethods(Method): Determines if the specified method is a listener deregistration method (for removing listeners).
getAdditionalInterfaces(): (Optional) Use this if you want to provide special support for your listeners.
getNotificationDelegates(): (Optional) Use this if needed to:
- Implement specific methods for your additional interfaces (it's often better to rely on default implementations in the interface itself).
- Override certain methods of ListenersNotifier (but consider if this is truly necessary).

For more details see JavaDoc (ListenerDefinitionDetector , AbstractDetector and MockoborContext.registerListenerDefinitionDetector)

See also Custom listener detector example, PropertyChangeDetector.java or TypicalJavaListenerDetector.java as implementation examples.

Using unsupported mocking tools

To redirect listener registration methods from a mocked observable object to the internal list of listeners, Mockobor requires the following:

Understand which mocking tool was used to mock the specified observable object.
Create a redirection mechanism using the detected mocking tool.

Mockobor provides out-of-the-box support for some mocking tools (see Dependencies).

If you are using a different mocking tool, you can add support for it by following these steps:

Create a custom implementation of ListenerRegistrationHandler.
Register it using MockoborContext.registerListenerRegistrationHandler.

For more details see JavaDoc (ListenerRegistrationHandler and MockoborContext.registerListenerRegistrationHandler)

See also MockitoListenerRegistrationHandler.java and EasymockListenerRegistrationHandler.java as implementation examples.

Restrictions

Only interfaces are accepted as listeners:
Methods like addMyListener(MyListener) will not be recognized as registration methods if MyListener is a class.
MyListener must be an interface. This is standard practice in Java.
Listener arrays and varargs are not supported:
Registration methods such as addMyListener(MyListener[] listeners) or addMyListener(MyListener... listeners) will also not be recognized as valid registration methods.

EasyMock restrictions

If you mock a collaborator object using EasyMock:

When mocking a collaborator object using EasyMock, keep the following restrictions in mind:

Notifier object creation:
A notifier object must be created (via Mockobor.createNotifierFor) before the tested object registers its listener through the mocked collaborator.
This is because registration methods must be redirected to the notifier before being invoked by the tested object.
As a result, it is not possible to inject mocks into the observer test object using the @TestSubject annotation.
Issues with varargs in listener methods:
If listener registration methods of the mocked collaborator object utilize varargs (e.g., addListener(MyListener l, Object... selector)), issues may arise. During recording mode, Mockobor cannot predict how many arguments will be passed during the actual invocation of such a method. Consequently, recorded and real invocations may not match. For more details, refer to this issue.

Installation

To use Mockobor in your unit tests, add the following dependency to your project.

maven

<dependency>
	<groupId>io.github.mickle-ak.mockobor</groupId>
	<artifactId>mockobor</artifactId>
	<version>1.1.4</version>
	<scope>test</scope>
</dependency>

gradle

testImplementation 'io.github.mickle-ak.mockobor:mockobor:1.1.4'  // groovy

testImplementation("io.github.mickle-ak.mockobor:mockobor:1.1.4")  // kotlin

For more details, refer to Maven Central.

Name		Name	Last commit message	Last commit date
Latest commit History 57 Commits
.github/workflows		.github/workflows
config		config
gradle/wrapper		gradle/wrapper
src		src
subprojects/dependencies-tests		subprojects/dependencies-tests
.gitignore		.gitignore
CHANGELOG.md		CHANGELOG.md
CONTRIBUTING.md		CONTRIBUTING.md
LICENSE		LICENSE
README.md		README.md
build.gradle.kts		build.gradle.kts
gradlew		gradlew
gradlew.bat		gradlew.bat
lombok.config		lombok.config
settings.gradle.kts		settings.gradle.kts

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Mockobor

Dependencies

Examples

simulate the sending of events from a mocked collaborator to the tested object

typical java style listeners

PropertyChangeListener

Observable, Observer

ensure complete deregistration of listeners

use Mockito annotations and Mockobor together

Detailed Usage

monitor a mocked observable object and verify the complete deregistration of its listeners

listener selectors

registration order

listener notifier settings

Extensions

Defining a Custom Listener Detector

Using unsupported mocking tools

Restrictions

EasyMock restrictions

Installation

maven

gradle

About

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mickle-ak/mockobor

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Mockobor

Dependencies

Examples

simulate the sending of events from a mocked collaborator to the tested object

typical java style listeners

PropertyChangeListener

Observable, Observer

ensure complete deregistration of listeners

use Mockito annotations and Mockobor together

Detailed Usage

monitor a mocked observable object and verify the complete deregistration of its listeners

listener selectors

registration order

listener notifier settings

Extensions

Defining a Custom Listener Detector

Using unsupported mocking tools

Restrictions

EasyMock restrictions

Installation

maven

gradle

About

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