doTestCollapseWithNoChange("xx");
  }

  private void doTestCollapse(String in, String out) {
    // Try a few different matchers which all match '-' and not 'x'
    // Try replacement chars that both do and do not change the value.
    for (char replacement : new char[] {'_', '-'}) {
      String expected = out.replace('_', replacement);
      assertEqualsSame(expected, in, is('-').collapseFrom(in, replacement));

    doTestCollapseWithNoChange("xx");
  }

  private void doTestCollapse(String in, String out) {
    // Try a few different matchers which all match '-' and not 'x'
    // Try replacement chars that both do and do not change the value.
    for (char replacement : new char[] {'_', '-'}) {
      String expected = out.replace('_', replacement);
      assertEqualsSame(expected, in, is('-').collapseFrom(in, replacement));