small changes to facilitate debugging

Author: fredrikt

src/pyff/pipes.py

@@ -146,6 +146,9 @@ def __init__(self, entry_point, req, store=None):
         self.req = req
         self.store = store
 
+    def __str__(self) -> str:
+        return f"<PipelineCallback to {self.req.plumbing}]>"
+
     def __copy__(self):
         return self
 

src/pyff/test/test_pipeline.py

@@ -69,7 +69,8 @@ def exec_pipeline(self, pstr):
         md = MDRepository()
         p = yaml.safe_load(six.StringIO(pstr))
         print("\n{}".format(yaml.dump(p)))
-        res = Plumbing(p, pid="test").process(md, state={'batch': True, 'stats': {}})
+        pl = Plumbing(p, pid="test")
+        res = pl.process(md, state={'batch': True, 'stats': {}})
         return res, md
 
     @classmethod