Java test class with many private methods [duplicate]

Question

I have a class that has the responsibility of importing contracts from a CSV to database.

The class itself has only one public method that starts the import and the other methods are all private (because only the class itself will use, and they hold the logic).

I'm starting to make tests for this class using Spock and there are many private methods, how should I test it?

Should I turn them into public to test? Test only the main method, the public one?

Whats the best?

Answer 1

You can use reflection to achieve this. The Method class has a method called setAcessible(boolean) which enables you to call it even if declared as private/protected/default. See the example below:

YourClass yourClassInstance = new YourClass();
Method yourMethod = YourClass.class.getDeclaredMethod("yourMethod", null);
yourMethod.setAccessible(true);
Object[] parameters = new Object[1];
parameters[0] = "A String parameter";
Object result = yourMethod.invoke(yourClassInstance, parameters);

Answer 2

In theory, your private methods are being used ultimately by one of the public methods, or else they're not used at all. So typically you setup your tests to call the public methods with the necessary context so that it hits your private methods.

The unit tests are primarily testing the compilation unit (i.e. the class). You can unit test methods directly but then they have to be public, which goes against having a nice clean API.

So test your public method enough to hit all the private methods. Private methods are internal mechanics of the class, they don't need to be tested directly.