The new TEST_P macro takes a function name and a "data" argument to
point to an arbitrary array of known size of test data. This allows
multiple tests to be run with different datasets. The array is stored
as a void * but advanced by a known size on each iteration.

The data for each invocation of the test is provided as a "data" argument,
it is the responsibility of the test to cast it to something sensible.

Also fixed single-test running to only run the tests specified