Merge pull request #43 from mateuscomp/tests

I will accept this pull request, but there are a lot of comments I have made.
Please, read them.
Merge pull request #44 from mateuscomp/tests

 Fixing some problems on merge #43
Removing the name 'default' of exception messages of instance tests
creation of test instanceWithValidValuesForTheConfigurationOfAttributesText
Merge between the previous versions