1 files changed, 110 insertions, 0 deletions
diff --git a/pylint/testutils/configuration_test.py b/pylint/testutils/configuration_test.py
new file mode 100644
index 000000000..2fac8f1c1
--- /dev/null
+++ b/pylint/testutils/configuration_test.py
@@ -0,0 +1,110 @@
+# Licensed under the GPL: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
+# For details: https://github.com/PyCQA/pylint/blob/main/LICENSE
+
+"""Utility functions for configuration testing."""
+import copy
+import json
+import logging
+import unittest
+from pathlib import Path
+from typing import Any, Dict, Tuple, Union
+from unittest.mock import Mock
+
+from pylint.lint import Run
+
+USER_SPECIFIC_PATH = Path(__file__).parent.parent.parent
+# We use Any in this typing because the configuration contains real objects and constants
+# that could be a lot of things.
+ConfigurationValue = Any
+PylintConfiguration = Dict[str, ConfigurationValue]
+
+
+def get_expected_or_default(
+    tested_configuration_file: str, suffix: str, default: ConfigurationValue
+) -> str:
+    """Return the expected value from the file if it exists, or the given default."""
+
+    def get_path_according_to_suffix() -> Path:
+        path = Path(tested_configuration_file)
+        return path.parent / f"{path.stem}.{suffix}"
+
+    expected = default
+    expected_result_path = get_path_according_to_suffix()
+    if expected_result_path.exists():
+        with open(expected_result_path, encoding="utf8") as f:
+            expected = f.read()
+        # logging is helpful to realize your file is not taken into
+        # account after a misspell of the file name. The output of the
+        # program is checked during the test so printing messes with the result.
+        logging.info("%s exists.", expected_result_path)
+    else:
+        logging.info("%s not found, using '%s'.", expected_result_path, default)
+    return expected
+
+
+EXPECTED_CONF_APPEND_KEY = "functional_append"
+EXPECTED_CONF_REMOVE_KEY = "functional_remove"
+
+
+def get_expected_configuration(
+    configuration_path: str, default_configuration: PylintConfiguration
+) -> PylintConfiguration:
+    """Get the expected parsed configuration of a configuration functional test"""
+    result = copy.deepcopy(default_configuration)
+    config_as_json = get_expected_or_default(
+        configuration_path, suffix="result.json", default="{}"
+    )
+    to_override = json.loads(config_as_json)
+    for key, value in to_override.items():
+        if key == EXPECTED_CONF_APPEND_KEY:
+            for fkey, fvalue in value.items():
+                result[fkey] += fvalue
+        elif key == EXPECTED_CONF_REMOVE_KEY:
+            for fkey, fvalue in value.items():
+                new_value = []
+                for old_value in result[fkey]:
+                    if old_value not in fvalue:
+                        new_value.append(old_value)
+                result[fkey] = new_value
+        else:
+            result[key] = value
+    return result
+
+
+def get_expected_output(configuration_path: str) -> Tuple[int, str]:
+    """Get the expected output of a functional test."""
+    output = get_expected_or_default(configuration_path, suffix="out", default="")
+    if output:
+        # logging is helpful to see what the expected exit code is and why.
+        # The output of the program is checked during the test so printing
+        # messes with the result.
+        logging.info(
+            "Output exists for %s so the expected exit code is 2", configuration_path
+        )
+        exit_code = 2
+    else:
+        logging.info(".out file does not exists, so the expected exit code is 0")
+        exit_code = 0
+    return exit_code, output.format(
+        abspath=configuration_path,
+        relpath=Path(configuration_path).relative_to(USER_SPECIFIC_PATH),
+    )
+
+
+def run_using_a_configuration_file(
+    configuration_path: Union[Path, str], file_to_lint: str = __file__
+) -> Tuple[Mock, Mock, Run]:
+    """Simulate a run with a configuration without really launching the checks."""
+    configuration_path = str(configuration_path)
+    args = ["--rcfile", configuration_path, file_to_lint]
+    # We do not capture the `SystemExit` as then the `runner` variable
+    # would not be accessible outside the `with` block.
+    with unittest.mock.patch("sys.exit") as mocked_exit:
+        # Do not actually run checks, that could be slow. We don't mock
+        # `Pylinter.check`: it calls `Pylinter.initialize` which is
+        # needed to properly set up messages inclusion/exclusion
+        # in `_msg_states`, used by `is_message_enabled`.
+        check = "pylint.lint.pylinter.check_parallel"
+        with unittest.mock.patch(check) as mocked_check_parallel:
+            runner = Run(args)
+    return mocked_exit, mocked_check_parallel, runner