Mocking Autowire in a class

Question

I have an XYZ class which is autowired in ABC and in class MyClass I have a method name doSomething() inside that method I do ABC abc = new ABC(); Then I call abc.someMethod();

Please see code sample below :

Class ABC

public class ABC {

  @Autowire
  private XYZ xyz;

  public void someMethod()
  {
   //Some stuff
   xyz.someFunc();

  }
}

Class MyCLass

public class MyCLass {

  public void doSomething() {
    ABC abc = new ABC();
    abc.someMethod();
  }
}

Need unit test doSomething() but I NPE as XYZ is null in ABC. How can I mock @Autowire in this case.

Just as an FYI, as soon as you use `new ABC()` to construct a bean, any Spring annotations will not work (i.e. autowiring will not work). See https://stackoverflow.com/questions/19896870/why-is-my-spring-autowired-field-null — dunni, Mar 01 '22 at 18:33

score 0 · Answer 1 · answered Mar 01 '22 at 18:36

If you use constructor injection instead of field injection, you can create the mock and give it to the constructor of ABC:

public class ABC {

    private final XYZ xyz;

    public ABC(XYZ xyz) {
        this.xyz = xyz;
    }

    public void someMethod()
    {
        //Some stuff
        xyz.someFunc();

    }
}

Then in your test, when you create the instance under test, you just create it and hand over the mock:

XYZ mock = mock(XYZ.class);

ABC underTest = new ABC(mock);

I dont have the access to modify the ABC code its owned by another entity. — StackFlowed, Mar 01 '22 at 19:32

Eddie Lopez · Answer 2 · 2022-03-02T17:09:31.553

You can use the following testing capabilities in your test:

import org.springframework.context.annotation.Configuration;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

Provide a configuration and use it, for example:

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = MyTest.MyTestConfiguration.class)
public class MyTest {

    // xyz injected into ABC and MyTest for convenience.
    @Autowired
    private XYZ xyz;

    @Test
    public void myTest() {
        // Some Stubbing...
        when(xyz.trySomething()).thenReturn(true);

        // Some verification.
        new ABC().doSomething();
        verify(xyz, times(1))
                .trySomething();
    }

    // Note it is used in @ContextConfiguration
    @Configuration
    static class MyTestConfiguration {
        @Bean
        XYZ xyz() {
            return mock(XYZ.class);
        }
    }
}

The documentation is a bit extensive, search for the mentioned annotations here https://docs.spring.io/spring-framework/docs/current/reference/html/testing.html#integration-testing

I just edited the answer, added `@RunWith(SpringJUnit4ClassRunner.class)`. I've used this plenty of times, though I may have missed some details. — Eddie Lopez, Mar 02 '22 at 17:10

Mocking Autowire in a class

2 Answers2