Mocking Java 使用 Mockito/JUnit 的常量变量（公共静态）

Question

I need to mock the constant variable in order to test one of my method. How can I do it with Mokito and Junit.

  @Component( "mybean" )
  @org.springframework.context.annotation.Scope( value="session" )  
  public class MyBean {

    Public void methodToBeTested() {
       if (!AppConst.SOME_CONST.equals(obj.getCostCode())) {
         // some logic
       }
    }
 }

AppConst class

@Configuration
public class AppConst
{
   public static  String  SOME_CONST;
   public static  String  HOST_URL;

   @PostConstruct
   public void postConstruct()
   {
     SOME_CONST = "My Code";
     HOST_URL  = "Some URL";

   }
}

So, from my junit test class, how can I mock the AppConst and it's variables? Now, when I run it, i hit a nullpointer error.

Can this be done with powermock? if yes please give some sample

Mockito version I use.

compile "org.mockito:mockito-all:1.9.5" compile "org.powermock:powermock-mockito-release-full:1.6.1"

Answer 1

Instead of mocking there would be another solution to be able to test it:

public void methodToBeTested(SomeObject obj) {
   performLogic(AppConst.SOME_CONST, obj);
}

boolean performLogic(String check, SomeObject testObj) {
   if (!check.equals(obj.getCostCode())) {
     // some logic
     return true;
   }
   return false;
}

That way you can test two things, both combined show you that your code works as intended:

public void testMethodToBeTested() {
    MyBean mb = new MyBean() {
        @Override
        void performLogic(String check, SomeObject testObj) {
            assertSame("check constant is passed", AppConst.SOME_CONST, check);
        }
    }
    mb.methodToBeTested(new SomeObject());

    mb = new MyBean();
    SomeObject so = createSomeTestObject("My Code"); // not the actual constant but an equal String
    assertFalse("check some logic not occurred", mb.performLogic("My Code", so));
    so = createSomeTestObject("Not the constant");
    assertFalse("check some logic not occurred", mb.performLogic("Not the constant", so));
    assertTrue("check some logic occurred", mb.performLogic("My Code", so));
    // additional tests covering the actual logic
}

Another solution could be putting the condition of the if-statement into its own method, eg shouldLogicOccurr(String check) and test that method individually.

In other words: Sometimes it's necessary to refactor your code to make tests easier or sometimes even possible at all. A good side effect is the next time you implement something you already have testability in mind and create your code suitable for this in the first place.

Mocking is a good way to get things under test that use third party libraries that can't be changed and have too many dependencies to be set up but if you end up using that for your own code you've got a design issue.