I have a Java class named, MyClass
, that I want to test with JUnit. The public method, methodA
, that I want to test calls a private method, methodB
, in the same class to determine which conditional path to follow. My goal is to write JUnit tests for the different paths in methodA
. Also, methodB
calls a service, so I do not want it to actually be executed when I run the JUnit tests.
What is the best way to mock methodB
and control its return so that I can test different paths for 'methodA'?
I prefer to use JMockit when writing mocks, so I am specifically interested in any answer that applies to JMockit.
Here is my example class:
public class MyClass {
public String methodA(CustomObject object1, CustomObject object2) {
if(methodB(object1, object2)) {
// Do something.
return "Result";
}
// Do something different.
return "Different Result";
}
private boolean methodB(CustomObject custObject1, CustomObject custObject2) {
/* For the sake of this example, assume the CustomObject.getSomething()
* method makes a service call and therefore is placed in this separate
* method so that later an integration test can be written.
*/
Something thing1 = cobject1.getSomething();
Something thing2 = cobject2.getSomething();
if(thing1 == thing2) {
return true;
}
return false;
}
}
This is what I have so far:
public class MyClassTest {
MyClass myClass = new MyClass();
@Test
public void test_MyClass_methodA_enters_if_condition() {
CustomObject object1 = new CustomObject("input1");
CustomObject object2 = new CustomObject("input2");
// How do I mock out methodB here to return true?
assertEquals(myClass.methodA(object1, object2), "Result");
}
@Test
public void test_MyClass_methodA_skips_if_condition() {
CustomObject object1 = new CustomObject("input1");
CustomObject object2 = new CustomObject("input2");
// How do I mock out methodB here to return false?
assertEquals(myClass.methodA(object1, object2), "Different Result");
}
}
Thanks!
Instead of using mock(class) here we need to use Mockito. spy() to mock the same class we are testing. Then we can mock the method we want as follows. Mockito.
For Mockito, there is no direct support to mock private and static methods. In order to test private methods, you will need to refactor the code to change the access to protected (or package) and you will have to avoid static/final methods.
Hi, I would strongly advice against mocking private inner classes since usually there are other more elegant ways of testing your problem and the test case can end up being very complex. Personally I would try to refactor the code if the test gets too complex or write an integration test instead of mocking at all.
Annotate the mehod with @testVisible: Use the TestVisible annotation to allow test methods to access private or protected members of another class outside the test class. These members include methods, member variables, and inner classes. This annotation enables a more permissive access level for running tests only.
Do not be tempted to mock private methods, even if you can engaging in trickery to do so using a mocking tool. Private members are implementation details, which you should be free to change. Instead use the non-private API to exercise the class. If this is troublesome, consider moving the troublesome code into a different class, if it is not there already, and use dependency injection to inject a mock implementation of the troublesome code.
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