How do I write the junit test for a thread pool executor configuration (AsyncConfig)?

Following is my configuration for a thread pool executor-

@Configuration
@EnableAsync
public class AsyncConfig {

    @Bean(name = "asyncExecutor")
    public Executor asyncExecutor() {   //should not return null
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(30);
        executor.setMaxPoolSize(30);
        executor.setQueueCapacity(1000);
        executor.setThreadNamePrefix("Async-");
        executor.initialize();
        return executor;
    }
}

I need to write a Unit test for the same. I do understand how to write unit tests for services and controllers, but being new to this stuff, I am not sure what to test in case of configurations. For instance in the above code I can verify that the return value of the function is not null. But I don't understand how to do that either, because no where in the project am I calling the 'asyncExecutor' function. All I am doing is annotating the function (that needs to be run using the thread pool executor) with

@Async("asyncExecutor")

Please help me with this, and also any other stuff that I can test for the same

You can use JUnit and Mockito to write a Unit test for this configuration bean. Example -

import static org.junit.jupiter.api.Assertions.assertNotNull;

import java.util.concurrent.Executor;

import org.junit.jupiter.api.Test;
import org.mockito.Mockito;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;

public class AsyncConfigTest {

    @Test
    public void testAsyncExecutor() {
        AsyncConfig asyncConfig = new AsyncConfig();
        Executor executor = asyncConfig.asyncExecutor();
        assertNotNull(executor);

        // Verify the executor properties
        ThreadPoolTaskExecutor threadPoolTaskExecutor = (ThreadPoolTaskExecutor) executor;
        assertEquals(30, threadPoolTaskExecutor.getCorePoolSize());
        assertEquals(30, threadPoolTaskExecutor.getMaxPoolSize());
        assertEquals(1000, threadPoolTaskExecutor.getQueueCapacity());
        assertEquals("Async-", threadPoolTaskExecutor.getThreadNamePrefix());
    }

}

Mokito to mock ThreadPoolTaskExecutor

import static org.mockito.Mockito.verify;

import org.junit.jupiter.api.Test;
import org.mockito.Mockito;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;

public class MyServiceTest {

    @Test
    public void testAsyncMethod() {
        // Create a mock of ThreadPoolTaskExecutor
        ThreadPoolTaskExecutor executorMock = Mockito.mock(ThreadPoolTaskExecutor.class);
        MyService myService = new MyService(executorMock);

        // Call the async method
        myService.doAsyncTask();

        // Verify that the executor was used
        verify(executorMock).execute(Mockito.any(Runnable.class));
    }

}

You're creating a mock ThreadPoolTaskExecutor object and passing it to your MyService class in the preceding test. Then you call an async method on the MyService class and check that the executor was used to perform the async task.