Scanner.nextLine() ignores whitespace? (Java)

I have a command-line game and am testing with JUnit, this is the test:

@Test
  public void testBattle() throws IOException{
    String input = "go forward\ngo left\ntake Pointy Stick\ngo backward\ngo " +
            "right\nnormal attack\nnormal attack\nquit\n";
    provideInput(input);
    actual = new File("src/main/testFiles/testBattle.txt");
    expected = new File("src/main/testFiles/testBattleExpected.txt");
    PrintStream o = new PrintStream(actual);
    System.setOut(o);

    ui.gameLoop();
    assertTrue(FileUtils.contentEqualsIgnoreEOL(actual, expected, null));

  }

And this is the provide input method:

 private void provideInput(String data) {
    String newdata = data.trim();
    testIn = new ByteArrayInputStream(newdata.getBytes());
    System.setIn(testIn);
  }

I'm doing scanner nextline so:

command = input.nextLine().toLowerCase().trim();

where "input" here represents the scanner object
but I'm still getting this error, specifically when the first "normal attack" is passed into System.in

java.util.NoSuchElementException: No line found

on that line above. I thought nextline ignored whitespace? If not did I format my string wrong to not include it?

EDIT:
From the first few lines of UI.gameLoop() I only initialize the scanner once.

public void gameLoop() throws IOException, JsonSyntaxException {
    input = new Scanner(System.in);
    engine = new GameEngine(path);

> I thought nextline ignored whitespace?

Nope. According to the javadocs, it reads past the next end-of-line sequence (or to EOF), and then returns everything up to but not including the end-of-line sequence.

If you are getting

java.util.NoSuchElementException: No line found

that means that the Scanner has already reached the end of the input stream, or (maybe) the Scanner is trying to read from an input stream that was prematurely closed somewhere else in your code.

We can make guesses about what the real problem is, but without seeing >>your<< minimal reproducible example, we can't take this much further.

Actually, I just spotted a clue:

> ... I am testing with JUnit ...

This is possibly at the root of your problems. A JVM can only "read to the end of System.in" once in its lifetime. If you have two or more JUnit tests that need to do this, it is going to be difficult, unless you can find a way to "mock" the System.in variable.

It may be simpler to reorganize your code so that you take the input from some stream that is passed to your game code as a parameter. By reorganizing you can make it easier to write unit tests.

There's not a lot to go on, but I'm guessing you're creating multiple Scanners, one for each time you want to read a line. This usually works ok interactively since humans are slow typers, but fails when each Scanner's readahead ends up consuming multiple lines.

You can see the difference in this MCVE:

import java.util.*;
import java.io.*;

class Foo {
  public static void main(String[] args) throws Exception {
    String newdata = "go forward\ngo left\ntake Pointy Stick\ngo backward\ngo " +
                  "right\nnormal attack\nnormal attack\nquit\n".trim();
    ByteArrayInputStream testIn = new ByteArrayInputStream(newdata.getBytes());
    System.setIn(testIn);

    boolean includeBug = Boolean.valueOf(args[0]);

    if (includeBug) {

      for(int i=0; i<8; i++) {
        Scanner input = new Scanner(System.in);
        System.out.println("Read: " + input.nextLine());
      }

    } else {

      Scanner input = new Scanner(System.in);
      for(int i=0; i<8; i++) {
        System.out.println("Read: " + input.nextLine());
      }

    }
  }
}

When includeBug is true, it creates a new Scanner for each line and crashes like you say. If it's false, it creates a single Scanner and works correctly:

$ javac Foo.java
$ java Foo true
Read: go forward
Exception in thread "main" java.util.NoSuchElementException: No line found
        at java.util.Scanner.nextLine(Scanner.java:1540)
        at Foo.main(Foo.java:17)

$ java Foo false
Read: go forward
Read: go left
Read: take Pointy Stick
Read: go backward
(etc)

Are you checking if it has a next line? With Scanners, you usually either have to handle the exception (not really something I'd prefer) or you have to use the hasNextLine() method to avoid the exception.

while (input.hasNextLine()) {
     command = input.nextLine().toLowerCase().trim();
}