Over a million developers have joined DZone.

Field Injection When Mocking Frameworks Fail

Learn more about field injection with mocking frameworks, and CDI in applications when unit testing Java classes.

· Java Zone

Microservices! They are everywhere, or at least, the term is. When should you use a microservice architecture? What factors should be considered when making that decision? Do the benefits outweigh the costs? Why is everyone so excited about them, anyway?  Brought to you in partnership with IBM.


You are using Dependency Injection (CDI) in your application and you want to unit test your Java classes without making it an integration test by using Weld or Arquillian. You are using a Mocking framework like Mockito or EasyMock but still have trouble getting all your dependencies injected into the class because one of the injections is a String type or another final class.

Cannot mock/spy class java.lang.String
Mockito cannot mock/spy following:
   - final classes
   - anonymous classes
   - primitive types

I personally came by this challenge after writing a couple of @Producer methods for injecting a property from a property file. So in effect I was injecting a String and I had trouble writing a test for it.


Create your own small injection utility method:

  public static void injectField(final Object injectable, 
                                 final String fieldname, 
                                 final Object value) {
      try {
          final java.lang.reflect.Field field = injectable.getClass()
          final boolean origionalValue = field.isAccessible();
          field.set(injectable, value);
      } catch (final NoSuchFieldException | IllegalAccessException e) {
          throw new RuntimeException(e.getMessage(), e);

So if you have a class like this, with an @Inject and no setter, you want to test:

package nl.ivonet.example;
import javax.inject.Inject;
public class Greeting {
    private String greeting;

    public String toString() {
        return this.greeting;

You can test it like this:

package nl.ivonet.example;
import org.junit.Test;
import static nl.ivonet.example.utility.CDI.injectField;
import static org.hamcrest.core.Is.is;
import static org.junit.Assert.assertThat;

public class GreetingTest {
    public void testToString() throws Exception {
        Greeting greeting = new Greeting();
        injectField(greeting, "greeting", "Hello, world");
        assertThat(greeting.toString(), is("Hello, world"));

For other Injectables, you can still use Mockito or your Mocking framework of choice but for final classes you can do the above.

Have fun,


Discover how the Watson team is further developing SDKs in Java, Node.js, Python, iOS, and Android to access these services and make programming easy. Brought to you in partnership with IBM.

java ,junit ,mock final class ,mock

Published at DZone with permission of Ivo Woltring. See the original article here.

Opinions expressed by DZone contributors are their own.

The best of DZone straight to your inbox.

Please provide a valid email address.

Thanks for subscribing!

Awesome! Check your inbox to verify your email so you can start receiving the latest in tech news and resources.

{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}