JUnit test for console input and output

Question

I have only one method main. How to check System.out.println() and replace Scanner to input values automatically using JUnit?

P.S. Please, provide some solutions...

Answer 1

Ideally, extract the awkward dependencies so that you can test without them. Change main to simply:

public static void main(String[] args) {
  doWork(new Scanner(System.in), System.out);
}

// TODO: Rename to something meaningful
public static void doWork(Scanner input, PrintStream output) {
  // Remainder of code
}

(Consider using a Writer instead of a PrintStream for output.)

Then you don't really need to unit test main - but you can test doWork using a Scanner based on a StringReader, and output based on a StringWriter, providing whatever input you want and checking the output.