updated package setup (#485)

* updated package setup

* updated to use python 3.9

* fixed test runner

* fixed typecheck tests

* fixed discrepencies

* added override to runner

* updated travis

* updated pre-commit hooks

* updated dep

tests/test_error_handling.py

@@ -0,0 +1,72 @@
+import tempfile
+import typing
+
+import pytest
+
+from mypy_django_plugin.main import extract_django_settings_module
+
+TEMPLATE = """usage: (config)
+...
+[mypy.plugins.django_stubs]
+    django_settings_module: str (required)
+...
+(django-stubs) mypy: error: 'django_settings_module' is not set: {}
+"""
+
+
+@pytest.mark.parametrize(
+    "config_file_contents,message_part",
+    [
+        pytest.param(
+            None,
+            "mypy config file is not specified or found",
+            id="missing-file",
+        ),
+        pytest.param(
+            ["[not-really-django-stubs]"],
+            "no section [mypy.plugins.django-stubs]",
+            id="missing-section",
+        ),
+        pytest.param(
+            ["[mypy.plugins.django-stubs]", "\tnot_django_not_settings_module = badbadmodule"],
+            "the setting is not provided",
+            id="missing-settings-module",
+        ),
+        pytest.param(
+            ["[mypy.plugins.django-stubs]"],
+            "the setting is not provided",
+            id="no-settings-given",
+        ),
+    ],
+)
+def test_misconfiguration_handling(capsys, config_file_contents, message_part):
+    #  type: (typing.Any, typing.List[str], str) -> None
+    """Invalid configuration raises `SystemExit` with a precise error message."""
+    with tempfile.NamedTemporaryFile(mode="w+") as config_file:
+        if not config_file_contents:
+            config_file.close()
+        else:
+            config_file.write("\n".join(config_file_contents).expandtabs(4))
+            config_file.seek(0)
+
+        with pytest.raises(SystemExit, match="2"):
+            extract_django_settings_module(config_file.name)
+
+    error_message = TEMPLATE.format(message_part)
+    assert error_message == capsys.readouterr().err
+
+
+def test_correct_configuration() -> None:
+    """Django settings module gets extracted given valid configuration."""
+    config_file_contents = [
+        "[mypy.plugins.django-stubs]",
+        "\tsome_other_setting = setting",
+        "\tdjango_settings_module = my.module",
+    ]
+    with tempfile.NamedTemporaryFile(mode="w+") as config_file:
+        config_file.write("\n".join(config_file_contents).expandtabs(4))
+        config_file.seek(0)
+
+        extracted = extract_django_settings_module(config_file.name)
+
+    assert extracted == "my.module"