It's for improving code coverage. If it's not called manually from the test, the success callback part of loading data using Lawnchair will never be called. This is because at the moment, manage is called at global setup. At that point, there will be no dataset in memory or saved locally (we are not actually saving any data during tests), so a new dataset will be created and saved (again, in memory). Next time when manage is called again, it will return the dataset from memory, the success callback of loadDataSet will never be covered.
But if we manually call loadDataSet, the success callback of Lawnchair loading will be invoked, thus improve the code coverage.