SampleControllerTest.java

import static org.hamcrest.Matchers.equalTo;
import static org.junit.Assert.assertThat;
import static org.mockito.Mockito.when;

import java.io.IOException;

import org.junit.Before;
import org.junit.Test;
import org.mockito.Mockito;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;

/**
 * Sample tests using mockito
 * 
 * @author ian.chen
 */
public class SampleControllerTest {

	// a controller to test
	private MyController controller;
	private MyService mockService;

	/**
	 * Will run before each test method
	 */
	@Before
	public void setUp() {
		// create a controller
		controller = new MyController();

		// create a mock of the backend
		mockService = Mockito.mock(MyService.class);

		// inject the mock
		controller.setService(mockService);

		// TODO perform other initialization here
	}
	
	/**
	 * Test happy case
	 */
	@Test
	public void sampleTest() throws Exception {
		// define the behaviour of the backend
		when(mockService.getMessage()).thenReturn("I am a mock");

		// Test the method
		ResponseEntity<String> response = controller.handleRequest();

		// check it was a 200
    	assertThat(response.getStatusCode(), equalTo(HttpStatus.OK));
    	// check the body is the the expected value
    	assertThat(response.getBody(), equalTo("I am a mock"));
	}
	
	/**
	 * Test error case
	 */
	@Test
	public void sampleError() throws Exception {
		// tell the backend to throw an exception
		when(mockService.getMessage())
			.thenThrow(new IOException());

		// This should throw an exception
		ResponseEntity<String> response = controller.handleRequest();
		
		// check an error response was received
    	assertThat(response.getStatusCode(), equalTo(HttpStatus.INTERNAL_SERVER_ERROR));
	}
	
	/**
	 * Test that an exception is thrown.
	 */
	@Test(expected = RuntimeException.class)
	public void sampleThrownException() throws Exception {
		// tell the backend to throw an uncaught exception
		when(mockService.getMessage())
			.thenThrow(new RuntimeException());

		// This should throw an exception
		controller.handleRequest();
	}

	/***************************
	 * Example classes to test *
	 ***************************/
	
	// a example of a service which needs to be injected
	interface MyService {
		public String getMessage() throws IOException;
	}

	// a example of a controller to test
	class MyController {
		private MyService service;
		public void setService(MyService service) {
			this.service = service;
		}

		public ResponseEntity<String> handleRequest() {
			try {
				return new ResponseEntity<String>(service.getMessage(), HttpStatus.OK);
			} catch (IOException e) {
				return new ResponseEntity<String>("An exception was thrown", HttpStatus.INTERNAL_SERVER_ERROR);				
			}

		}
		
	}
}