Create proper tests involving datasets, with expected results which have been manually confirmed as good

[rbejar]

Many tests in DataTestsSpec are essentially smoke tests, and the results produced by them must be checked manually (e.g., loading the resulting datasets in QGIS and validating what you see/measure/query there) if you need to be sure that they produce the correct results. Curating a set of test datasets, with the expected results after the different transformations, and using that in the tests to make sure that the results are what is expected is pending work.