BUG: fix dummy ControlLayer shims side-effect

Since ControlLayer sets its .shims to SHIMS by default, setting
attributes in dummy cl .shims changes SHIMS for the rest of the
test session. Creating a new dict for the dummy_shim fixture avoids
this side-effect.

For redundancy, I also changed ControlLayer.__init__ to copy SHIMS
instead of using the global instance.

superscore/control_layers/core.py

@@ -32,7 +32,7 @@ class ControlLayer:
     def __init__(self, *args, shims: Optional[List[str]] = None, **kwargs):
         if shims is None:
             # load all available shims
-            self.shims = SHIMS
+            self.shims = SHIMS.copy()
             logger.debug('No shims specified, loading all available communication '
                          f'shims: {list(self.shims.keys())}')
         else:

superscore/tests/conftest.py

@@ -742,8 +742,7 @@ def monitor(self, *args, **kwargs):
 @pytest.fixture(scope='function')
 def dummy_cl() -> ControlLayer:
     cl = ControlLayer()
-    cl.shims['ca'] = DummyShim()
-    cl.shims['pva'] = DummyShim()
+    cl.shims = {protocol: DummyShim() for protocol in ['ca', 'pva']}
     return cl