Add a few tests to validate config parsing

tests/integration/test_aggregator.py

@@ -1,14 +1,19 @@
 """Test aggregation of config files and command-line options."""
 import os
 
+import mock
 import pytest
 
+from flake8 import defaults
 from flake8.main import options
 from flake8.options import aggregator
 from flake8.options import config
 from flake8.options import manager
 
 CLI_SPECIFIED_CONFIG = 'tests/fixtures/config_files/cli-specified.ini'
+USER_CONFIG = 'tests/fixtures/config_files/user-config.ini'
+LOCAL_CONFIG = 'tests/fixtures/config_files/local-config.ini'
+MISSING_CONFIG = 'tests/fixtures/config_files/missing.ini'
 
 
 @pytest.fixture
@@ -22,6 +27,70 @@ def optmanager():
     return option_manager
 
 
+def mock_config_finder(program='flake8', arguments=[],
+                       prepend_configs=[], append_configs=[],
+                       user_config='', local_configs=[]):
+    """Create a config finder with controlled access to files."""
+    config_finder = config.ConfigFileFinder(
+        program, arguments, prepend_configs, append_configs)
+
+    config_finder.user_config_file = mock.Mock(return_value=user_config)
+    config_finder.generate_possible_local_files = mock.Mock(
+        return_value=local_configs
+    )
+
+    return config_finder
+
+
+@pytest.mark.parametrize('config_finder_params,options_assertions', [
+    # Default values with no config file
+    ({}, {
+        "select": {'E', 'W', 'F', 'C90'},
+        "ignore": set(defaults.IGNORE),
+        "max_line_length": 79,
+    }),
+    # Correct values with user config only
+    ({'user_config': USER_CONFIG}, {
+        "select": {'E', 'W', 'F', 'C90'},
+        "ignore": ['D203'],
+        "max_line_length": 79,
+    }),
+    # Default values with missing user config file
+    ({'user_config': MISSING_CONFIG}, {
+        "select": {'E', 'W', 'F', 'C90'},
+        "ignore": set(defaults.IGNORE),
+        "max_line_length": 79,
+    }),
+    # Correct values with local config only
+    ({'local_configs': [LOCAL_CONFIG]}, {
+        "select": {'E', 'W', 'F'},
+        "ignore": set(defaults.IGNORE),
+        "max_line_length": 79,
+    }),
+    # Default values with missing local config file
+    ({'local_configs': [MISSING_CONFIG]}, {
+        "select": {'E', 'W', 'F', 'C90'},
+        "ignore": set(defaults.IGNORE),
+        "max_line_length": 79,
+    }),
+])
+def test_aggregate_options_resulting_values(
+        optmanager, config_finder_params, options_assertions
+):
+    """Verify we get correct values with various config files combinations."""
+    arguments = []
+    config_finder = mock_config_finder(**config_finder_params)
+    parsed_options, args = aggregator.aggregate_options(
+        optmanager, config_finder, arguments
+    )
+
+    for option, expected_value in options_assertions.items():
+        # Cast the option to the expected value type, especially for sets
+        expected_type = type(expected_value)
+        option_value = getattr(parsed_options, option)
+        assert expected_value == expected_type(option_value)
+
+
 def test_aggregate_options_with_config(optmanager):
     """Verify we aggregate options and config values appropriately."""
     arguments = ['flake8', '--config', CLI_SPECIFIED_CONFIG, '--select',