capture-mocked-arguments.md

User

How do you capture the argument used for mockito mock call?

Assistant

In Mockito, you can capture the arguments used in mock calls using the ArgumentCaptor class. This is useful when you want to verify the arguments passed to a method on a mock object. Here's a step-by-step guide on how to use ArgumentCaptor:

1. Add Mockito to your project: If you haven't already, you need to add the Mockito library to your project. If you're using Maven, you can add the following dependency to your pom.xml:

   <dependency>
       <groupId>org.mockito</groupId>
       <artifactId>mockito-core</artifactId>
       <version>4.0.0</version>
       <scope>test</scope>
   </dependency>

   If you're using Gradle, add this to your build.gradle:

   testImplementation 'org.mockito:mockito-core:4.0.0'

2. Create a test class and use ArgumentCaptor: Here's an example of how to use ArgumentCaptor to capture arguments passed to a mock method:

   import org.junit.jupiter.api.Test;
   import org.mockito.ArgumentCaptor;
   import org.mockito.Mockito;
   
   import static org.junit.jupiter.api.Assertions.assertEquals;
   import static org.mockito.Mockito.*;
   
   public class ArgumentCaptorTest {
   
       // Define an interface for demonstration purposes
       interface MyService {
           void doSomething(String arg);
       }
   
       @Test
       public void testArgumentCaptor() {
           // Create a mock of MyService
           MyService myService = Mockito.mock(MyService.class);
   
           // Call the method on the mock
           myService.doSomething("Hello, Mockito!");
   
           // Create an ArgumentCaptor for the String argument
           ArgumentCaptor<String> argumentCaptor = ArgumentCaptor.forClass(String.class);
   
           // Verify that the method was called and capture the argument
           verify(myService).doSomething(argumentCaptor.capture());
   
           // Get the captured argument
           String capturedArgument = argumentCaptor.getValue();
   
           // Assert that the captured argument is as expected
           assertEquals("Hello, Mockito!", capturedArgument);
       }
   }

In this example:

1. We define an interface MyService with a method doSomething.
2. We create a mock of MyService using Mockito.mock.
3. We call the doSomething method on the mock with a specific argument.
4. We create an ArgumentCaptor for the String type.
5. We use verify to check that the doSomething method was called on the mock and capture the argument passed to it.
6. We retrieve the captured argument using argumentCaptor.getValue.
7. We assert that the captured argument matches the expected value.

This approach can be used to capture and verify arguments of any type passed to methods on mock objects.

---

User

create a testng example test with generated arguments

Assistant

Certainly! Below is an example of how to create a TestNG test with generated arguments using the @DataProvider annotation. This example will also demonstrate how to use Mockito and ArgumentCaptor to capture and verify arguments.

1. Add dependencies: Ensure you have the necessary dependencies for TestNG and Mockito in your project. If you're using Maven, add the following to your pom.xml:

   <dependencies>
       <dependency>
           <groupId>org.testng</groupId>
           <artifactId>testng</artifactId>
           <version>7.4.0</version>
           <scope>test</scope>
       </dependency>
       <dependency>
           <groupId>org.mockito</groupId>
           <artifactId>mockito-core</artifactId>
           <version>4.0.0</version>
           <scope>test</scope>
       </dependency>
   </dependencies>

   If you're using Gradle, add this to your build.gradle:

   testImplementation 'org.testng:testng:7.4.0'
   testImplementation 'org.mockito:mockito-core:4.0.0'

2. Create the test class with a @DataProvider and a test method:

   import org.mockito.ArgumentCaptor;
   import org.mockito.Mockito;
   import org.testng.annotations.DataProvider;
   import org.testng.annotations.Test;
   
   import static org.mockito.Mockito.verify;
   import static org.testng.Assert.assertEquals;
   
   public class MyServiceTest {
   
       // Define an interface for demonstration purposes
       interface MyService {
           void doSomething(String arg);
       }
   
       // DataProvider that generates test data
       @DataProvider(name = "testData")
       public Object[][] createData() {
           return new Object[][] {
               { "Hello, Mockito!" },
               { "TestNG with Mockito" },
               { "Argument Captor Example" }
           };
       }
   
       // Test method that uses the DataProvider
       @Test(dataProvider = "testData")
       public void testDoSomething(String input) {
           // Create a mock of MyService
           MyService myService = Mockito.mock(MyService.class);
   
           // Call the method on the mock with the input argument
           myService.doSomething(input);
   
           // Create an ArgumentCaptor for the String argument
           ArgumentCaptor<String> argumentCaptor = ArgumentCaptor.forClass(String.class);
   
           // Verify that the method was called and capture the argument
           verify(myService).doSomething(argumentCaptor.capture());
   
           // Get the captured argument
           String capturedArgument = argumentCaptor.getValue();
   
           // Assert that the captured argument is as expected
           assertEquals(capturedArgument, input);
       }
   }

In this example:

1. Interface Definition: We define an interface MyService with a method doSomething.
2. DataProvider: We create a @DataProvider method named createData that generates test data. This method returns a 2D array of objects, where each inner array represents a set of arguments for a test method.
3. Test Method: We create a test method testDoSomething that uses the @DataProvider. The test method takes a String argument, which is provided by the @DataProvider.
4. Mockito and ArgumentCaptor: Inside the test method, we create a mock of MyService, call the doSomething method on the mock with the input argument, and use ArgumentCaptor to capture and verify the argument passed to the method.
5. Assertion: We assert that the captured argument matches the input argument provided by the @DataProvider.

This setup allows you to run the test method multiple times with different sets of arguments generated by the @DataProvider.