Adding regression tests.

Currently coverings for datastore.

@rakyll if the approach is ok I'll add to the README instructions on how to run the tests (basically configuring the export variables in run_regression_tests.sh) and I will add the tests to our build.
Race condition again.

We just need to assert there are numeric IDs, all you can do is to perform a getAll with the retrieved keys to see if save has been successful.