A good test is a test covering well existing code, using small amount of lines
of code an which is fast to run.
Whenever possible, it's important to organize the code into distinct parts
(documents, classes , methods) that could be tested separately. Like this
every part could be easily modified and tested without checking the whole code
It is not necessary to test huge amount of data. Let's say you would like to
test the method setTitle on a document, checking a very few values is enough
(like simple ascii value and utf8 values with a string in Japanese), you do
not need to test various complete dictionaries.