Context
- In a TDD environment, the same coding standards should be enforced on Unit Test code as on application code. Often, however this isn’t the case! Remember: unit tests can contain technical debt too!
- Mocking service calls with EasyMock involves repetitive code.
- This repetitive code can be simplified, and rendered more fluent with the Builder pattern.
Benefits of a MockBuilder
- Sharpened focus: unit tests becomes more focussed on the code under test , rather than code written to support or prepare the test.
- Cheaper to write more and more tests.
First Iteration: mocking a service call to the ClientService with EasyMock
Consider an example of a unit test where there is a call to the ClientService that we want to replace with a call to a Mock:
@Test
public void testLoadPresetFormWithClient() throws RemoteException {
NewBusinessApplication nba = NewBusinessApplicationBuilder.create()
.withPresetOwner()
.build();
nba.getOwner().setRegisteredAddress(null);
nba.getOwner().setClientNumber("12345678");
Client stubbedClient = new Client();
stubbedClient.setAddress(new Address());
stubbedClient.getAddress().setLine1("Client Address 1");
stubbedClient.getAddress().setLine2("Client Address 2");
stubbedClient.getAddress().setLine3("Client Address 3");
stubbedClient.getAddress().setLine4("Client Address 4");
stubbedClient.getAddress().setLine5("Client Address 5");
ClientService mockClientService = EasyMock.createMock(ClientService.class);
EasyMock.expect(mockClientService.findByClientNumber((String)EasyMock.anyObject())).andReturn(stubbedClient).anyTimes();
EasyMock.replay(mockClientService);
EasyMock.verify(mockClientService);
ClientServiceDelegate.getInstance().setClientService(mockClientService);
EmployerCorrespondenceDetailsForm form = service.loadPresetForm(nba);
assertFormAndClientRegisteredAddressEquals(form,mockClientService.findByClientNumber("12345678"));
assertFormAndApplicationBusinessAddressEquals(form,nba);
}
The vast majority of the code in this unit test is support code, written to mock the client service call, and ensure a stubbed client is used for the purposes of the test.
In fact , only the last three lines of this test method are actual test code, executing the method under test, and evaluating the results
Second Iteration: Create ClientServiceMockBuilder
All the semi-boilerplate EasyMock code related to mocking the client service is now moved to it’s own object, where the builder pattern is implemented:
public class ClientServiceMockBuilder {
private ClientService mockClientService;
public static ClientServiceMockBuilder create() {
return new ClientServiceMockBuilder();
}
public ClientService build() {
EasyMock.replay(mockClientService);
EasyMock.verify(mockClientService);
return mockClientService;
}
private ClientServiceMockBuilder() {
mockClientService = EasyMock.createMock(ClientService.class);
}
public ClientServiceMockBuilder withFindByClientNumberStubbedClient(){
try{
EasyMock.expect(mockClientService.findByClientNumber((String)EasyMock.anyObject())).andReturn(createStubbedClient()).anyTimes();
} catch(RemoteException e){
throw new RuntimeException(e);
}
return this;
}
private Client createStubbedClient(){
Client client = new Client();
client.setAddress(new Address());
client.getAddress().setLine1("Client Address 1");
client.getAddress().setLine2("Client Address 2");
client.getAddress().setLine3("Client Address 3");
client.getAddress().setLine4("Client Address 4");
client.getAddress().setLine5("Client Address 5");
return client;
}
}
Revisiting the Unit Test, it is now a lot cleaner, and more readable. More to the point though, we are pointing the way to any unit test that needs to mock a call to the Client Service:
@Test
public void testLoadPresetForm_WithClient() throws RemoteException {
NewBusinessApplication nba = NewBusinessApplicationBuilder.create()
.withPresetOwner()
.build();
nba.getOwner().setRegisteredAddress(null);
nba.getOwner().setClientNumber("12345678");
ClientService mockClientService = ClientServiceMockBuilder.create()
.withFindByClientNumberStubbedClient()
.build();
ClientServiceDelegate.getInstance().setClientService(mockClientService);
EmployerCorrespondenceDetailsForm form = service.loadPresetForm(nba);
assertFormAndClientRegisteredAddressEquals(form,mockClientService.findByClientNumber("12345678"));
assertFormAndApplicationBusinessAddressEquals(form,nba);
}
Third Iteration: Abstract out common MockBuilder behaviour
If your unit test code involves the use of many different mocked objects, you’ll be building a lot of MockBuilder objects to correspond with these. You’ll also quickly notice repetition of certain code, which can be abstracted to an abstract parent class called MockBuilder, as below:
public abstract class MockBuilder<T extends Object> {
protected T mockedObject;
public T build() {
EasyMock.replay(mockedObject);
EasyMock.verify(mockedObject);
return mockedObject;
}
}
The updated ClientServiceMockBuilder now looks like this:
public class ClientServiceMockBuilder extends MockBuilder<ClientService> {
public static ClientServiceMockBuilder create() {
return new ClientServiceMockBuilder();
}
private ClientServiceMockBuilder() {
mockedObject = EasyMock.createMock(ClientService.class);
}
public ClientServiceMockBuilder withFindByClientNumberStubbedClient(){
try{
EasyMock.expect(mockedObject.findByClientNumber((String)EasyMock.anyObject())).andReturn(createStubbedClient()).anyTimes();
} catch(RemoteException e){
throw new RuntimeException(e);
}
return this;
}
private Client createStubbedClient(){
Client client = new Client();
client.setAddress(new Address());
client.getAddress().setLine1("Client Address 1");
client.getAddress().setLine2("Client Address 2");
client.getAddress().setLine3("Client Address 3");
client.getAddress().setLine4("Client Address 4");
client.getAddress().setLine5("Client Address 5");
return client;
}
}
And we can extend the MockBuilder again as required. For example, here’s another implementation, a Spring MVC BindingResultMockBuilder
public class BindingResultMockBuilder extends MockBuilder<BindingResult> {
public BindingResultMockBuilder() {
mockedObject = EasyMock.createMock(BindingResult.class);
}
public static BindingResultMockBuilder create() {
return new BindingResultMockBuilder();
}
public BindingResultMockBuilder withErrors(boolean hasErrors) {
EasyMock.expect(mockedObject.hasErrors()).andReturn(hasErrors).anyTimes();
return this;
}
public BindingResultMockBuilder withAddAllErrors() {
mockedObject.addAllErrors((Errors) EasyMock.anyObject());
EasyMock.expectLastCall().anyTimes();
return this;
}
public BindingResultMockBuilder withGetAllFieldErrors() {
EasyMock.expect(mockedObject.getFieldErrors()).andReturn(new ArrayList<FieldError>()).anyTimes();
return this;
}
public BindingResultMockBuilder withRejectValue() {
mockedObject.rejectValue((String) EasyMock.anyObject(), (String) EasyMock.anyObject());
EasyMock.expectLastCall().anyTimes();
return this;
}
}
Results
- The MockBuilder can be extended to create a new subclass for anything you need to mock.
- Large amounts of boilerplate code can be refactored into a simpler invocation of a Builder.
- Cleaner Unit Tests = Better Unit Tests.
Paddy Corry's Blog 