code: def _generate_fixture_tuples():
      """Return fixture tuples for pytest_generate_tests."""
      # collect fixture tuples here
      fixture_tuples = []
  
      for scitype in SCITYPES:
          # if we know there are no conversions defined, skip this scitype
          if scitype in SCITYPES_NO_CONVERSIONS:
              continue
  
          conv_mat = _conversions_defined(scitype)
  
          mtypes = scitype_to_mtype(scitype, softdeps="exclude")
  
          if len(mtypes) == 0:
              # if there are no mtypes, this must have been reached by mistake/bug
              raise RuntimeError(
                  "no mtypes defined for scitype " + scitype
              )
  
          # by convention, number of examples is the same for all mtypes of the scitype
          examples = get_examples(
              mtype=mtypes[0], as_scitype=scitype, return_lossy=True
          )
          n_fixtures = len(examples)
  
          # there must be fixtures for each scitype, otherwise there is a bug in the tests
          if n_fixtures == 0:
              raise RuntimeError(
                  "no fixtures defined for scitype " + scitype
              )
  
          for to_type in mtypes:
              for from_type in mtypes:
                  for i in range(n_fixtures):
                      # only add if conversion is implemented
                      if conv_mat[to_type][from_type]:
                          fixture_tuples += [
                              (scitype, from_type, to_type, i)
                          ]
  
      return fixture_tuples
  
imports: from sktime.datatypes import SCITYPE_REGISTER, scitype_to_mtype
  from sktime.datatypes._convert import _conversions_defined, convert
  from sktime.datatypes._examples import get_examples
  from sktime.utils._testing.deep_equals import deep_equals
label_desc: Use image node_id 1 for calling a global function with example usage: _generate_fixture_tuples() and returns: fixture_tuples