docs: def get_each_choice(self, cls=None, **kwargs):
          """Returns a generator that generates positive cases by
          "each choice" algorithm.
          """
          defaults = {attr: kwargs[attr][0] for attr in kwargs}
          for set_of_values in izip_longest(*kwargs.values()):
              case = cls() if cls else self._CasesClass()
              for attr, value in izip(kwargs.keys(), set_of_values):
                  if value is None:
                      value = defaults[attr]
                  setattr(case, attr, value)
              yield case