public void TestPrevious()
{
Tokenizer tokenizer = new Tokenizer(new ExpressionDictionary(), @"@book{ aaker:1912,
author = { tes~est }
}");
Assert.Throws<ArgumentOutOfRangeException>(() => tokenizer.GetPreviousCharacters(10));
tokenizer.NextToken();
tokenizer.NextToken();
tokenizer.NextToken();
tokenizer.NextToken();
tokenizer.NextToken();
AbstractToken token = tokenizer.NextToken();
Assert.AreEqual(" author ", tokenizer.GetPreviousCharacters(10));
}