how can I access a private method from the test class

Question

I have some methods which are private in the class example and I want to use them in the test class for testing purposes, how can I access these methods and leave them as private

import java.util.*;

public class Example
{
      Scanner scanner;
    public Example()
    {
       scanner = new Scanner(System.in);
    }
    private void enterName()
    {
        System.out.println("Enter name");
        String name = scanner.nextLine();
        System.out.println("Your name is: " + name);
    }
    private void enterAge()
    {
         System.out.println("Enter age");
        int age = scanner.nextInt();
        System.out.println("Your age is : " + age); 
    }
    public void userInput()
    {
        enterAge();
        enterName();
    }
}


public class Test
{

  public static void main(String args[])
  {
      Example n = new Example();
      n.enterName();
      n.enterAge();
    }

}

yeah, but the test class is used for testing all the methods individually, is it possible to use protected — Arif Muni, Oct 29 '13 at 18:31
that's not possible. private methods are limited only to the class. — Isuru Gunawardana, Oct 29 '13 at 18:31
http://stackoverflow.com/questions/34571/whats-the-proper-way-to-test-a-class-with-private-methods-using-junit?rq=1 — MadConan, Oct 29 '13 at 18:32
is it right to extends the class example, and make the methods in the class as protected or, is it wrong — Arif Muni, Oct 29 '13 at 18:33
you can make it protected and access from the test class, but what is the point? — Isuru Gunawardana, Oct 29 '13 at 18:46
Just call `n.userInput();` as this calls them individually. This is not an automated test as you need use input and you don't check the result in code. I can see what you are trying to do but it not clear to me what difference it will make. — Peter Lawrey, Oct 29 '13 at 19:51

Bart · Answer 1 · 2013-10-29T19:09:44.063

Why would you test the private methods while one will only use the public one? Unit testing is about testing for expected behavior. Public methods expose that behavior.

If you want to test the output generated you could implement a protected method to write to out e.g.

public class Example {

    // code omitted 

    private void enterName() {
        writeMessage("Enter name");
        String name = scanner.nextLine();
        writeMessage("Your name is: " + name);
    }

    protected void writeMessage(String msg) {
        System.out.println(msg);
    }
}

In your test you could then create a private class which extends Example and overrides the writeMessage method.

public class ExampleTest {

    public testOutput() {
        MyExample e = new MyExample();
        e.userInput();

        String output = e.getOutput();

        // test output string
    }

    private class MyExample extends Example {
        private String output = "";

        public String getOutput() {
            return output;
        }

        @Override
        public void writeMessage(String msg) {
            output += msg;
        }
    }
}

You also might want a setter or constructor which can inject the Scanner object. This will make testing easier since you could then inject a mocked scanner version.

score 0 · Answer 2 · answered Oct 29 '13 at 19:13

Unit-testing is indeed black-box testing, so you cannot, and should not, access the private (inner mechanisms) methods. However, white-box testing is often called assertion-based verification. Just put assertions (or it-then-throw statements) everywhere, and your black-box unit test will become a white-box test.

More specifically, try to put pre-conditions and post-conditions as much as possible in your private methods to verify the inputs and the outputs. Therefore, you define a contract between every method caller and callee. If something goes wrong, you'll quickly see where and why.

See Design-by-Contract for more info!

how can I access a private method from the test class

2 Answers2

You also might want a setter or constructor which can inject the Scanner object. This will make testing easier since you could then inject a mocked scanner version.