ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

Inject a mock with JUnit

Updated on October 16, 2011

Inject that Mock!

I want to show you a trick to inject mock in a class when you can't (or just hate) to add get/set methods to the code that is to be tested.

If you are familiar with testing, in particular with Java/JUnit, you already know that to test a class in isolation, the base requirement is creating mocks of the classes that "collaborate" with the class you want to test, and inject the created mocks in it.

For example in this simple case:

package org.sample;
 
public class Client {
     
    private Service simpleService;
     
    public Client() {
        simpleService = new Service();
    }
     
    public String hello() {
        return simpleService.sayHello("Daniele");
    }
 
}
package org.sample;
 
public class Service {
 
    public String sayHello(String name) {
        return "Hello " + name;
    }
 
}

I want to test the class org.sample.Client mocking the simpleService instance of the class org.sample.Service. One of the things I can do to inject the mock of the Service class is adding a 'set' method to the Client class, like this:

public void setService (Service service) {
	this.simpleService = service;
}

Sometimes you can't (it's happened to me working for some companies :)) or maybe you just don't want to add this kind of method to the application code. So, how can I test in isolation without it? In my test-tool-box I added this "utils" class:

package org.sample;
 
import java.lang.reflect.Field;
 
public class ReflectionUtils {
 
    public static Object getField(Object o, String fieldName) {
        Field field = getAccessibleField(fieldName, o.getClass());
        Object fieldValue = null;
        try {
            fieldValue = field.get(o);
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
        return fieldValue;
    }
 
    public static void setField(Object o, String fieldName, Object inject) {
        Field field = getAccessibleField(fieldName, o.getClass());
        try {
            field.set(o, inject);
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
    }
 
    // search in class, in case superclasses as well
    private static Field getAccessibleField(String fieldName, Class c) {
        Field field = null;
        while (c != null) {
            try {
                field = c.getDeclaredField(fieldName);
                field.setAccessible(true);
                break;
            } catch (NoSuchFieldException e) {
                c = c.getSuperclass();
            }
        }
        return field;
    }
}

Using it, we will get this test class:

package org.sample;
 
import static org.junit.Assert.*;
 
import org.junit.Before;
import org.junit.Test;
 
public class ClientTest {
     
    private Client client;
     
    @Before
    public void setUpMyStuff() {
        client = new Client();
        Service mock = new ServiceMock();
	// in place of client.setService(mock); we have:
        ReflectionUtils.setField(client, "simpleService", mock);
    }
 
    @Test
    public void hello() {
        assertEquals("Goodbye Daniele", client.hello());
    }
 
    // you can use something like Mockito to create a mock
    private class ServiceMock extends Service {
        @Override
        public String sayHello(String name) {
            return "Goodbye " + name;
        }
    }
}

In this test the "Service" class is mocked and the mock replaces the message "Hello Daniele" with "Goodbye Daniele". To inject the mock I've used:

public static void setField(Object o, String fieldName, Object inject)

in the ReflectionUtils class. Respectively the 3 parameters passed in the method are:

  • The instance of the class to test (or the class that needs a mock)
  • The name of the property inside the class that represents the class to mock
  • The mock instance

Try to run the test above un/commenting the line of code:

ReflectionUtils.setField(client, "simpleService", mock);

Enjoy!

Comments

    0 of 8192 characters used
    Post Comment
    • NitroD profile imageAUTHOR

      NitroD 

      8 years ago from London

      Glad it helped you :)

    • profile image

      jchacana 

      8 years ago

      Man, you saved my day. I was unable to use Arquillian with this legacy code but your snippet made it possible to inject dependencies. Thank you!

    working

    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, hubpages.com uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at: https://corp.maven.io/privacy-policy

    Show Details
    Necessary
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the googleapis.com or gstatic.com domains, for performance and efficiency reasons. (Privacy Policy)
    Features
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Marketing
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Statistics
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)
    ClickscoThis is a data management platform studying reader behavior (Privacy Policy)