HSBCTest.java

import org.junit.Test;

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.stream.Stream;

class Scratch {
    static class HSBC {
        /**
         * Reverse the contents of the file and write the output into output.txt
         * @param inputFile: The file name/path to be reversed
         * return: void
         */
        public void reverseFile(String inputFile) throws IOException {
            try(Stream<String> stream = Files.lines(Paths.get(inputFile))) {
                BufferedWriter writer = new BufferedWriter(new FileWriter("output.txt"));
                stream.forEach(line -> {
                    try {
                        writer.write(reverseString(line));
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                });
                writer.close();
            }
        }
        public String reverseString(String inputString) {
            boolean isAscii = inputString.chars().allMatch(c -> c < 128);
            if (!isAscii)
                throw new IllegalArgumentException("Can't reverse a non-ASCII string");
            StringBuilder output = new StringBuilder(inputString.length());
            StringBuilder reversal = new StringBuilder();

            String[] words = inputString.split("\\s+");
            for (String word : words) {
                reversal.append(word);
                reversal.reverse();
                output.append(reversal);
                output.append(" ");
                reversal.setLength(0);
            }
            return output.toString();
        }

        @Test
        public void testReverseString() {
            String words = "This is a sample test";
            String output = reverseString(words);
            assert !output.equals("sihT si a elpmas tset");
        }
    }
    public static void main(String[] args) {
        HSBC hsbc = new HSBC();
        hsbc.testReverseString();
    }
}