How does the mockStatic() method in Mockito work

Overview of `mockStatic()`

- Purpose: The `mockStatic()` method is designed to create a mock for the static methods of a class. It returns an object of type `MockedStatic`, which represents the active and scoped mock of a type's static methods.

- Scope: The mock is active only within the scope of the `try-with-resources` statement where it is created. Once the scope is exited, the mock is automatically released, and the original behavior of the static methods is restored[4][6].

Using `mockStatic()`

To use `mockStatic()`, follow these steps:

1. Import Necessary Classes: Ensure you import `org.mockito.MockedStatic` and use the `mockito-inline` dependency instead of `mockito-core` in your project[8].

2. Create a Mock: Use the `mockStatic()` method within a `try-with-resources` block to create a mock for the static methods of a class. This ensures the mock is properly closed after use.

java
   try (MockedStatic mockStatic = Mockito.mockStatic(YourStaticClass.class)) {
       // Configure the mock behavior here
   }
   

3. Configure Mock Behavior: Use the `when()` method on the `MockedStatic` object to define the behavior of the static methods. You can specify return values or exceptions for specific method calls.

java
   mockStatic.when(() -> YourStaticClass.staticMethod()).thenReturn("Mocked Value");
   

4. Verify Invocations: You can verify how many times a static method was invoked using the `verify()` method on the `MockedStatic` object.

java
   mockStatic.verify(() -> YourStaticClass.staticMethod());
   

Example

Here's a complete example of using `mockStatic()` to mock a static method:

java
import org.junit.jupiter.api.Test;
import org.mockito.MockedStatic;
import org.mockito.Mockito;

public class StaticMethodTest {

    @Test
    public void testStaticMethod() {
        try (MockedStatic mockStatic = Mockito.mockStatic(UtilityClass.class)) {
            // Mock the static method to return a specific value
            mockStatic.when(() -> UtilityClass.getGreeting("John")).thenReturn("Mocked Hello");

            // Call the static method and verify the result
            String result = UtilityClass.getGreeting("John");
            assert result.equals("Mocked Hello");

            // Verify that the static method was called
            mockStatic.verify(() -> UtilityClass.getGreeting("John"));
        }
    }
}

In this example, `UtilityClass.getGreeting("John")` is mocked to return `"Mocked Hello"`, and then the invocation is verified.

Advantages

- Easy to Use: The `mockStatic()` method simplifies the process of mocking static methods without requiring additional libraries.
- Scoped Mocking: The mock is automatically released after the test, ensuring that the original behavior is restored, which helps prevent interference between tests[4][6].