Protocols: fix mutation of overrides (#650)

Currently the `overrides` input dictionary provided to the
`get_builder_from_protocol` method can be mutated to also include the
defaults from the protocol. Here we make a copy of the `right`
dictionary in the `recursive_merge` function, to prevent the key/value
pairs of the `left` dictionary to be added to the `right` one. This
prevents the mutation of the `overrides` argument.

aiida_quantumespresso/workflows/protocols/utils.py

@@ -70,6 +70,9 @@ def recursive_merge(left, right):
     """
     import collections
 
+    # Note that a deepcopy is not necessary, since this function is called recusively.
+    right = right.copy()
+
     for key, value in left.items():
         if key in right:
             if isinstance(value, collections.abc.Mapping) and isinstance(right[key], collections.abc.Mapping):

tests/workflows/protocols/test_utils.py

@@ -0,0 +1,15 @@
+# -*- coding: utf-8 -*-
+"""Tests for the utility functions for the protocols."""
+
+
+def test_recursive_merge():
+    """Test the recursive merge function."""
+    from aiida_quantumespresso.workflows.protocols.utils import recursive_merge
+
+    left_dict = {'a': {'b': 1, 'c': {'d': 2}}, 'g': 3}
+    right_dict = {'a': {'c': {'d': 'D'}}, 'e': {'f': 'F'}}
+    merged = recursive_merge(left_dict, right_dict)
+
+    assert right_dict == {'a': {'c': {'d': 'D'}}, 'e': {'f': 'F'}}
+
+    assert merged == {'a': {'b': 1, 'c': {'d': 'D'}}, 'e': {'f': 'F'}, 'g': 3}