unit-testing

Fix Mockito void method exception errors with doThrow(). Learn correct syntax for mocking void methods to throw exceptions, JUnit examples, verification, ArgumentCaptor, spies, and best practices for unit tests.

Use Mockito spy for partial mocking in Java to mock specific methods like getPrice() and getQuantity() while letting getValue() execute real logic in Stock class. Step-by-step guide with doReturn examples and JUnit tests.