Preparing comprehensive unit and integration tests

[reiniervlinschoten]

In this pull request I was working on developing comprehensive unit and integration tests.
For the following tests I have updated the tests:

• getStudyData
• getStudyDataPoints (only the call with the default parametrization)
• getStudyDataBulk, getStudyDataPointsBulk
• getField, getFieldsPages, getFields
• getParticipant, getParticipantsPages, getParticipants

These functions need updated tests. These test_that files are also marked with TODO:

• getStudyDataPoints (with different parameters)
• getForm, getForms, getFormsPages
• getRepeatingData, getRepeatingDatasPages, getRepeatingDataForm, getRepeatingDataFormsPages, getRepeatingDataForms
• getStudyDataPoint, getStudyDataPointsPages, getStudyDataPoints
• getStudy, getStudiesPages, getStudies
• getSurvey, getSurveysPages, getSurveys
• getVisit, getVisitsPages, getVisits

The following need new unit tests as they are important in getStudyData:

• adjustTypes
• adjustCheckboxFields
• generateFieldMetadata
• cols_to_map
• transformOptionGroupsInternal

The tests are currently being ran on PythonWrapperTest - Study, which I also use to test the PythonWrapper. Access to the study can be granted by me or @martijnkersloot. No data in this study should be changed or tests will fail. If tests have to write to a database, they can use PythonWrapperTest - Client (Write).