Testing class that insert, update and delete from the db

Question

I have class that has 3 methods: insert, update and delete from the db. In order to test it in the insert test method I need to use the insert method and after I insert i need to delete what I inserted, but in order to delete I should use the delete method that I also want to test so it didn't make sense to me that I need to use them and also test them.

I hope you understand my problem. Thanks in advance!

Answer 1

You must decide what you want to test. That was you describe, it is an integration test. By a “real” unitTest, you test only your method, and not the System method and not the database.

If you want a unitTest, you have several options. For Example, you work with interfaces and catch your statement before it comes to the database.

Edit 1 - one possibility to implement unit test with interfaces:

You need one interface that implements the method these go to the backend system:

public interface IDatabase{

    public returnValue insert(yourParam);

    public int update(yourParam);

}

Then you implement your method with the real functions in a class:

public class Database implements IDatabase {

    @Override
    public returnValue insert(yourParam) {
        // do something
        return null;
    }

    @Override
    public int update(yourParam){
        // do something
        return 0;
    }    
}

This class you call in the main class:

/**
 * The real class to do what you want to do.
 */
public class RealClass {

private IDatabase dbInstance = null;

    private IDatabase getDbInstance() {
        if (dbInstance == null) {
            dbInstance = new Database();
        }
        return dbInstance;
    }

    protected void setDbInstance(IDatabase dataBase) {
        dbInstance = dataBase;
    }

    public static void main(String[] args) {
        getDbInstance().insert(yourParam);

    }
}

For the unit test you implement the interface again:

public class UnitTest implements IDatabase {

    @Override
    public returnValue insert(yourParam) {
        // Here can you test your statement and manipulate the return value
        return null;
    }

    @Override
    public int update(yourParam){
        if (yourParam.containsValue(value1)) {
          assertEquals("yourStatement", yourParam);
          return 1;
        }else if (yourParam.containsValue(value2)) {
          assertEquals("yourStatement2", yourParam);
          return 5;
        }else{
           assertTrue(false,"unknown Statement")
        }
    }

    @Test
    public void yourTest(){
       RealClass.setDbInstance(this);
        //Test something
    }        
}

This is time-consuming to implement, but with this, you are independent from the backend system and you can call the unittest every time without a database.