@Test
  public void nullObjectInExt() {

    thrown.expectMessage("Null isn't correct object to format");
    StringFormatterDoubleExtension ext = new StringFormatterDoubleExtension();
    ext.format(new StringBuilder(), null, ".2");
  }
  @Test
  public void nullBufferInExt() {

    thrown.expectMessage("Buffer == null");
    StringFormatterDoubleExtension ext = new StringFormatterDoubleExtension();
    Double a = 0.0;
    ext.format(null, a, ".2");
  }
  @Test
  public void nullPatternInExt() {

    thrown.expectMessage("Pattern must be non empty string");
    StringFormatterDoubleExtension ext = new StringFormatterDoubleExtension();
    Double a = 0.0;
    ext.format(new StringBuilder(), a, null);
  }