Can anyone please provide me an example showing how to use the org.mockito.ArgumentCaptor
class and how it is different from simple matchers that are provided with mockito.
I read the provided mockito documents but those doesn't illustrate it clearly, none of them are able to explain it with clarity.
I agree with what @fge said, more over. Lets look at example. Consider you have a method:
class A {
public void foo(OtherClass other) {
SomeData data = new SomeData("Some inner data");
other.doSomething(data);
}
}
Now if you want to check the inner data you can use the captor:
// Create a mock of the OtherClass
OtherClass other = mock(OtherClass.class);
// Run the foo method with the mock
new A().foo(other);
// Capture the argument of the doSomething function
ArgumentCaptor<SomeData> captor = ArgumentCaptor.forClass(SomeData.class);
verify(other, times(1)).doSomething(captor.capture());
// Assert the argument
SomeData actual = captor.getValue();
assertEquals("Some inner data", actual.innerData);
The two main differences are:
when you capture even a single argument, you are able to make much more elaborate tests on this argument, and with more obvious code;
an ArgumentCaptor can capture more than once.
To illustrate the latter, say you have:
final ArgumentCaptor<Foo> captor = ArgumentCaptor.forClass(Foo.class);
verify(x, times(4)).someMethod(captor.capture()); // for instance
Then the captor will be able to give you access to all 4 arguments, which you can then perform assertions on separately.
This or any number of arguments in fact, since a VerificationMode
is not limited to a fixed number of invocations; in any event, the captor will give you access to all of them, if you wish.
This also has the benefit that such tests are (imho) much easier to write than having to implement your own ArgumentMatcher
s -- particularly if you combine mockito with assertj.
Oh, and please consider using TestNG instead of JUnit.
The steps in order to make a full check are :
First, prepare the argument captor :
ArgumentCaptor<ArgumentClass> argumentCaptor = ArgumentCaptor.forClass(ArgumentClass.class);
Second, verify the call to the dependent on component (collaborator of subject under test).
times(1) is the default value, so ne need to add it.
verify(dependentOnComponent, times(1)).method(argumentCaptor.capture());
Third, get the argument passed to collaborator using getValue() of the captor
ArgumentClass someArgument = messageCaptor.getValue();
Fourth, use someArgument for assertions
I created this example that simulates a very simple service that uses a repository to save a String (no dependency injection, no entities), just to teach ArgumentCaptor quickly.
The service receives, converts to uppercase and trim a name, then invoke the repository.
The repository "saves" the String.
With ArgumentCaptor I want to know which value is passed to the repository and then check if it's trimmed and in uppercase, as expected
3 classes: PersonService, PersonRepository and PersonServiceTest (packages omitted)
public class PersonService {
private PersonRepository personRepository;
public void setPersonRepository(final PersonRepository personRepository) {
this.personRepository = personRepository;
}
public void savePerson(final String name) {
this.personRepository.save(name.toUpperCase().trim());
}
}
public class PersonRepository {
public void save(final String person) {
System.out.println(".. saving person ..");
}
}
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.times;
import static org.mockito.Mockito.verify;
import org.junit.jupiter.api.Test;
import org.mockito.ArgumentCaptor;
class PersonServiceTest {
@Test
void testPersonService() {
// Create the repository mock
final PersonRepository personRepositoryMock = mock(PersonRepository.class);
// Create the service and set the repository mock
final PersonService personService = new PersonService();
personService.setPersonRepository(personRepositoryMock);
// Save a person
personService.savePerson("Mario ");
// Prepare an ArgumentCaptor to capture the value passed to repo.saveMethod
final ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
// Capture the argument passed in the unique method invocation
verify(personRepositoryMock, times(1)).save(captor.capture());
// Check if the captured value is the expected one
final String capturedParameter = captor.getValue();
assertEquals("MARIO", capturedParameter);
}
}
Here I am giving you a proper example of one callback method . so suppose we have a method like method login() :
public void login() {
loginService = new LoginService();
loginService.login(loginProvider, new LoginListener() {
@Override
public void onLoginSuccess() {
loginService.getresult(true);
}
@Override
public void onLoginFaliure() {
loginService.getresult(false);
}
});
System.out.print("@@##### get called");
}
I also put all the helper class here to make the example more clear: loginService class
public class LoginService implements Login.getresult{
public void login(LoginProvider loginProvider,LoginListener callback){
String username = loginProvider.getUsername();
String pwd = loginProvider.getPassword();
if(username != null && pwd != null){
callback.onLoginSuccess();
}else{
callback.onLoginFaliure();
}
}
@Override
public void getresult(boolean value) {
System.out.print("login success"+value);
}}
and we have listener LoginListener as :
interface LoginListener {
void onLoginSuccess();
void onLoginFaliure();
}
now I just wanted to test the method login() of class Login
@Test
public void loginTest() throws Exception {
LoginService service = mock(LoginService.class);
LoginProvider provider = mock(LoginProvider.class);
whenNew(LoginProvider.class).withNoArguments().thenReturn(provider);
whenNew(LoginService.class).withNoArguments().thenReturn(service);
when(provider.getPassword()).thenReturn("pwd");
when(provider.getUsername()).thenReturn("username");
login.getLoginDetail("username","password");
verify(provider).setPassword("password");
verify(provider).setUsername("username");
verify(service).login(eq(provider),captor.capture());
LoginListener listener = captor.getValue();
listener.onLoginSuccess();
verify(service).getresult(true);
also dont forget to add annotation above the test class as
@RunWith(PowerMockRunner.class)
@PrepareForTest(Login.class)
captor
defined in your answer?
Success story sharing
doSomething(data)
mutatesinnerData
, then will that change be present inassertEquals("Some inner data", actual.innerData)
, or willinnerData
be captured as-is beforedoSomething
is executed?OtherClass
is a mock, and as it is defined now thedoSomething()
will not actualy do anything, it simply records the object that was passed. This means that it will be captured as-is beforedoSomething
is executed.verify
,times(1)
is the default and can be omitted.verify
method, it uses that information to run matches against the verification that you are doing. For every parameter it asks whether it matches the specific call it checks. When ArgumentCaptor is checked, it simply stores the values it was invoked with so whenverify
ends, it holds all the relevant invocations. It's roughly how it works. Hope it helps