JUnit Test - BufferedReader Input Redirection

Question

I'm new to JUnit tests and I've written code to redirect a file as an input, but I'm not sure how to test it. What's the best way to test the code?

private static String request;

public static void main(String[] args) {
   readFile();
}

public static void readFile() {

    try {
       /* BufferedReader to read text from an input stream */
       BufferedReader input = new BufferedReader(new InputStreamReader(System.in));

       /* While loop to read each line of the file. request - each line is a different client request */ 
       while ((request = input.readLine()) != null) {
        System.out.println("Client request: " + request);
       }

       /* Closes input */
       input.close();
    }
    catch (Exception e) {
        e.printStackTrace();
    }
}

Does this answer your question? [JUnit: How to simulate System.in testing?](https://stackoverflow.com/questions/1647907/junit-how-to-simulate-system-in-testing) — Progman, Nov 16 '22 at 17:12

score 0 · Answer 1 · answered Nov 16 '22 at 17:03

System.in is a static field. Here are some steps to test your class:

Create a mock PrintStream.
In a method annotated with @BeforeAll, save the current System.in value.
In a method annotated with @BeforeAll, set System.in to your mock.
In a method annotated with @AfterAll, set System.in to the saved value from line 2 above.

JUnit Test - BufferedReader Input Redirection

1 Answers1