Allow undefined environment variables in config.

astrality/config.py

@@ -214,7 +214,15 @@ def insert_environment_values(
     env_variable_pattern = re.compile(r'\$\{(\w+)\}')
 
     def expand_environment_variable(match: Match[str]) -> str:
-        return env_dict[match.groups()[0]]
+        env_variable = match.groups()[0]
+        try:
+            return env_dict[env_variable]
+        except KeyError:
+            logging.error(
+                f'Could not insert environment variable {env_variable}. '
+                'It is not defined. Leaving it as is in the configuration.'
+            )
+            return '${' + env_variable + '}'
 
     return env_variable_pattern.sub(
         expand_environment_variable,

astrality/tests/test_config.py

@@ -134,6 +134,14 @@ def test_insert_environment_variables():
     expected = 'value2'
     assert insert_environment_values(upper_case_conficting_key) == expected
 
+def test_inserting_environment_variable_that_does_not_exist(caplog):
+    config_line= 'key=value-${DOES_NOT_EXIST}'
+    assert insert_environment_values(config_line) == config_line
+
+    assert caplog.record_tuples[0][2] == \
+        'Could not insert environment variable DOES_NOT_EXIST. ' \
+        'It is not defined. Leaving it as is in the configuration.'
+
 def test_insert_context_section():
     context = compiler.context({'context/section1': {'key_one': 'value_one'}})
     assert context['section1']['key_one'] == 'value_one'