anchor.diff:      [Test]
       [Ignore]
       procedure empty_ISBN;
  +
  +    [Test]
  +    [Ignore]
  +    procedure input_is_9_characters;
  +
  +    [Test]
  +    [Ignore]
  +    procedure invalid_characters_are_not_ignored;
     end;
   
   implementation
  
positive.code: 
      [Test]
      [Ignore]
      procedure isbn_without_check_digit;
  
      [Test]
  
negative.code: 
  procedure ISBNVerifierTest.empty_ISBN;
  begin
    Assert.IsFalse(TIsbn.isValid(''));
  end;
  
  procedure ISBNVerifierTest.input_is_9_characters;
  begin
    Assert.IsFalse(TIsbn.isValid('134456729'));
  end;
  
  procedure ISBNVerifierTest.invalid_characters_are_not_ignored;
  begin
    Assert.IsFalse(TIsbn.isValid('3132P34035'));
  end;
  
  procedure ISBNVerifierTest.invalid_character_in_isbn;
  begin
    Assert.IsFalse(TIsbn.isValid('3-598-P1581-X'));
  end;
  
  procedure ISBNVerifierTest.invalid_isbn_check_digit;
  