Argument captors in JUnit - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an argument captor in unit testing?

An argument captor is a tool used in unit testing to capture the arguments passed to a mock method, so you can inspect or assert their values later.

beginner

How do you declare an argument captor in JUnit with Mockito?

You declare it using @Captor annotation or by calling ArgumentCaptor.forClass(ClassName.class). For example: @Captor ArgumentCaptor<String> captor;

intermediate

Why use argument captors instead of verifying method calls directly?

Argument captors let you check the exact values passed to a method, especially when you want to assert on complex objects or multiple calls, which simple verification cannot do.

intermediate

Show a simple example of capturing an argument with Mockito in JUnit.

Example: 1. Declare captor: @Captor ArgumentCaptor<String> captor; 2. Call method on mock. 3. Verify and capture: verify(mock).method(captor.capture()); 4. Assert: assertEquals("expected", captor.getValue());

intermediate

Can argument captors capture multiple arguments from multiple calls?

Yes, argument captors can capture all arguments from multiple calls using captor.getAllValues(), which returns a list of all captured arguments in order.

What is the main purpose of an argument captor in unit testing?

A To capture and inspect arguments passed to mock methods

B To create mock objects automatically

C To verify the number of times a method was called

D To generate test data

Argument captors are used to capture the actual arguments passed to mock methods so you can check their values.

Which Mockito annotation is used to declare an argument captor?

A @Mock

B @Spy

C @InjectMocks

D @Captor

The @Captor annotation declares an argument captor in Mockito.

How do you retrieve all captured arguments from an argument captor?

A captor.getValue()

B captor.getAllValues()

C captor.values()

D captor.captureAll()

captor.getAllValues() returns a list of all arguments captured from multiple calls.

Which of the following is NOT a benefit of using argument captors?

A Verifying method call count

B Inspecting complex argument values

C Capturing arguments from multiple calls

D Asserting on argument properties

Verifying method call count is done by verify(mock, times(n)), not by argument captors.

In Mockito, after capturing an argument, how do you verify the method was called with that argument?

A verify(mock).method(captor.getValue())

B captor.verify(mock).method()

C verify(mock).method(captor.capture())

D mock.verify(captor.capture())

You use verify(mock).method(captor.capture()) to capture the argument during verification.

Explain what an argument captor is and why it is useful in unit testing with mocks.

Think about how you check what data a mock method received.

Describe the steps to use an argument captor in a JUnit test with Mockito.

Consider the flow from setup to assertion.