Unable to get BufferedReader to advance past the use of a Scanner object in an external java file

Question

I am trying to write a program that acts as an automatic grader that will

1. run a student's java file
2. write it's output to a text file
3. test that text file against another text file with the desired output

I haven't gotten past step 1 as when the BufferedReader gets to a line where the student program is waiting for the user to give input, it will not advance. I understand that I need to provide input, and I have created a BufferedWriter to provide it, but it's not taking it the way I expect it to. Let's say I have this file as the student's program:

import java.util.Scanner;
public class studentProgramTest {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);

        System.out.print("Enter any word: ");
        String word = in.next();

        System.out.println("The word is " + word);
    }
}

What I have so far for the auto grader is

public class hw3Grader {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        try {

            String program = "studentProgramTest.java";

            runProcess("java " + program);
        } catch (Exception e) {
            System.out.println(e);
        }
    }

    private static void runProcess(String command) throws Exception {
        Process pro = Runtime.getRuntime().exec(command);
        InputStreamReader stdout = new InputStreamReader(pro.getInputStream());
        OutputStreamWriter stdin = new OutputStreamWriter(pro.getOutputStream());

        BufferedReader in = new BufferedReader(stdout);
        BufferedWriter writer = new BufferedWriter(stdin);

        String line = null;
        while ((line = in.readLine()) != null) {
            System.out.println(line);
            if (line.contains("Enter any word:")) {
                writer.write("test\r");
                writer.flush();
                writer.close();
            }
        }
    }
}

From what I can discern, the reader is stuck between System.out.print("Enter any word: "); and String word = in.next(); as what I have noticed is that if I change System.out.print("Enter any word: "); to System.out.println("Enter any word: "); I am able to write a value for input and I get the output of the program. I've been thinking that maybe what I actually need to do, is check the line of code rather than the printed output. I have found this post to turn the InputStream into a String, and tried option 3, but it's still getting stuck at the same line, I'm assuming. I feel like there is something I am unaware of on how the code is actually working, so if anyone can provide any insight, that would be great!

What I have written to recreate option 3:

Scanner s = new Scanner(pro.getInputStream());
while (s.hasNextLine()) {
    if (s.nextLine().contains(".next()")) {
        System.out.println("test");
    }
}