How to test abstract class in Java with JUnit

Question

I am new to Java testing with JUnit  I have to work with Java and I would like to use unit tests   My problem is  I have an abstract class with some abstract methods  But there are some methods which are not abstract  How can I test this class with JUnit  Example code  very simple    abstract class Car        public Car int speed  int fuel            this speed   speed          this fuel   fuel             private int speed      private int fuel       abstract void drive         public int getSpeed             return this speed             public int getFuel             return this fuel            I want to test getSpeed   and getFuel   functions   Similar question to this problem is here  but it is not using JUnit   In JUnit FAQ section  I found this link  but I don t understand what the author want to say with this example  What does this line of code mean   public abstract Source getSource

User · Answer

Create a concrete class that inherits the abstract class and then test the functions the concrete class inherits from the abstract class

User · Answer

My way of testing this is quite simple  within each abstractUnitTest java  I simply create a class in the abstractUnitTest java that extend the abstract class  And test it that way

User · Answer

I would create a jUnit inner class that inherits from the abstract class  This can be instantiated and have access to all the methods defined in the abstract class    public class AbstractClassTest      public void testMethod                     class ConcreteClass extends AbstractClass

User · Answer

As an option  you can create abstract test class covering logic inside abstract class and extend it for each subclass test  So that in this way you can ensure this logic will be tested for each child separately

User · Answer

With the example class you posted it doesn t seem to make much sense to test getFuel   and getSpeed   since they can only return 0  there are no setters    However  assuming that this was just a simplified example for illustrative purposes  and that you have legitimate reasons to test methods in the abstract base class  others have already pointed out the implications   you could setup your test code so that it creates an anonymous subclass of the base class that just provides dummy  no-op  implementations for the abstract methods   For example  in your TestCase you could do this   c   new Car            void drive                Then test the rest of the methods  e g    public class CarTest extends TestCase       private Car c       public void setUp                 c   new Car                 void drive                              public void testGetFuel                  assertEquals c getFuel    0                         This example is based on JUnit3 syntax  For JUnit4  the code would be slightly different  but the idea is the same

User · Answer

You could do something like this  public abstract MyAbstractClass         Autowire     private MyMock myMock               protected String sayHello                 return myMock getHello            getName               public abstract String getName          this is your JUnit test public class MyAbstractClassTest extends MyAbstractClass         Mock     private MyMock myMock        InjectMocks     private MyAbstractClass thiz   this       private String myName   null        Override     public String getName             return myName              Test     public void testSayHello             myName    Johnny          when myMock getHello    thenReturn  Hello            String result   sayHello            assertEquals  Hello  Johnny   result

User · Answer

You can not test whole abstract class  In this case you have abstract methods  this mean that they should be implemented by class that extend given abstract class    In that class programmer have to write the source code that is dedicated for logic of his    In other words there is no sens of testing abstract class because you are not able to check the final behavior of it    If you have major functionality not related to abstract methods in some abstract class  just create another class where the abstract method will throw some exception

User · Answer

If you need a solution anyway  e g  because you have too many implementations of the abstract class and the testing would always repeat the same procedures  then you could create an abstract test class with an abstract factory method which will be excuted by the implementation of that test class  This examples works or me with TestNG   The abstract test class of Car   abstract class CarTest       the factory method abstract Car createCar int speed  int fuel       all test methods need to make use of the factory method to create the instance of a car  Test public void testGetSpeed         Car car   createCar 33  44       assertEquals car getSpeed    33             Implementation of Car  class ElectricCar extends Car        private final int batteryCapacity       public ElectricCar int speed  int fuel  int batteryCapacity            super speed  fuel           this batteryCapacity   batteryCapacity                   Unit test class ElectricCarTest of the Class ElectricCar   class ElectricCarTest extends CarTest           implementation of the abstract factory method     Car createCar int speed  int fuel            return new ElectricCar speed  fuel  0                 here you cann add specific test methods

User · Answer

You can instantiate an anonymous class and then test that class   public class ClassUnderTest Test        private ClassUnderTest classUnderTest       private MyDependencyService myDependencyService        Before     public void setUp   throws Exception           this myDependencyService   new MyDependencyService            this classUnderTest   getInstance               private ClassUnderTest getInstance             return new ClassUnderTest                     private ClassUnderTest init                      MyDependencyService myDependencyService                                 this myDependencyService   myDependencyService                  return this                              Override             protected void myMethodToTest                     return super myMethodToTest                            init myDependencyService             Keep in mind that the visibility must be protected for the property myDependencyService of the abstract class ClassUnderTest   You can also combine this approach neatly with Mockito  See here

User · Answer

If you have no concrete implementations of the class and the methods aren t static whats the point of testing them  If you have a concrete class then you ll be testing those methods as part of the concrete class s public API    I know what you are thinking  I don t want to test these methods over and over thats the reason I created the abstract class   but my counter argument to that is that the point of unit tests is to allow developers to make changes  run the tests  and analyze the results  Part of those changes could include overriding your abstract class s methods  both protected and public  which could result in fundamental behavioral changes  Depending on the nature of those changes it could affect how your application runs in unexpected  possibly negative ways  If you have a good unit testing suite problems arising from these types changes should be apparent at development time

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