TEST: remove duck-typing in save

src/stpipe/step.py

@@ -519,25 +519,10 @@ def run(self, *args):
                     for idx, result in enumerate(results_to_save):
                         if len(results_to_save) <= 1:
                             idx = None
-                        if isinstance(result, AbstractDataModel):
-                            self.save_model(result, idx=idx, format=self.name_format)
-                        elif hasattr(result, "save"):
-                            try:
-                                output_path = self.make_output_path(
-                                    idx=idx, name_format=self.name_format
-                                )
-                            except AttributeError:
-                                self.log.warning(
-                                    "`save_results` has been requested, but cannot"
-                                    " determine filename."
-                                )
-                                self.log.warning(
-                                    "Specify an output file with `--output_file` or set"
-                                    " `--save_results=false`"
-                                )
-                            else:
-                                self.log.info("Saving file %s", output_path)
-                                result.save(output_path, overwrite=True)
+                        if not isinstance(result, AbstractDataModel):
+                            # what has a "save"? Does anything ever reach this code
+                            raise Exception(f"Something has a save: {result}")
+                        self.save_model(result, idx=idx, format=self.name_format)
 
                 if not self.skip:
                     self.log.info("Step %s done", self.name)