There is no single, clear-cut test for deciding whether a worker classified as an IC is actually an employee. Different legal tests are used by various government agencies, including:
Each of these agencies is concerned with worker classification for different reasons, and has different rules and practices. Each agency normally makes classification decisions on its own and need not consider what other agencies have done, which means that one agency may find that a worker is an IC while another decides that he or she is an employee. It's also possible, though rare, for a worker to be deemed an IC in one state and an employee in another.
To find out the rules these agencies use, see Independent Contractor or Employee: How Government Agencies Make the Call.