String separator = System.getProperty("line.separator");
    sink.writeLines(lines);

    assertContainsExpectedLines(separator);
  }

  public void testWriteLines_specificSeparator() throws IOException {
    String separator = "\r\n";
    sink.writeLines(lines, separator);

    assertContainsExpectedLines(separator);
  }

  public void testWriteLinesStream_systemDefaultSeparator() throws IOException {

    String separator = System.getProperty("line.separator");
    sink.writeLines(lines);

    assertContainsExpectedLines(separator);
  }

  public void testWriteLines_specificSeparator() throws IOException {
    String separator = "\r\n";
    sink.writeLines(lines, separator);

    assertContainsExpectedLines(separator);
  }

  private void assertContainsExpectedString() throws IOException {