การจับอาร์กิวเมนต์ด้วย ArgumentCaptor

Sometimes verifying that a method was called is not enough. You need to assert on the actual argument the code constructed and passed. Mockito's ArgumentCaptor grabs that value for inspection.

Argument matchers like eq(...) check inputs during verification. A captor instead records the argument so you can run rich assertions afterward.

Declare a captor for the type you expect to capture.

Pass the captor's capture() where the argument would go inside verify.

After verification, retrieve the captured object and assert on its fields.

Here we confirm the service builds the correct user before saving it.

If the method was called several times, use getAllValues() to get every captured argument in order.

You can declare captors as fields with @Captor when using the Mockito extension, reducing boilerplate.

Use a matcher for simple equality checks at call time. Reach for a captor when the argument is complex, built internally, or needs multiple assertions.

Captors couple tests to internal construction details. Prefer them for genuinely complex arguments, not for everything, to keep tests resilient.

Captors let you verify the precise data your code hands to collaborators, catching subtle mapping or transformation bugs.

How do you retrieve the captured argument after verification?

You learned argument capturing:

• ArgumentCaptor.forClass or @Captor creates a captor
• Pass capture() inside verify
• getValue() / getAllValues() read the captured data
• Use captors for complex, internally built arguments