refactor: introduce MRTConfigError and decouple MRTFixture from pytest (#24)

* chore: bump version to 1.0.1

* refactor: introduce MRTConfigError and decouple MRTFixture from pytest

- Add pytest_mrt/exceptions.py with MRTException base and MRTConfigError
- MRTFixture.__init__ now raises MRTConfigError instead of calling
  pytest.fail() directly — core logic no longer depends on pytest
- mrt fixture wrapper catches MRTConfigError and converts to pytest.fail()
  keeping clean test output while preserving layer separation

* fix: sort imports in plugin.py to satisfy ruff

Author: croc100

pytest_mrt/exceptions.py

@@ -0,0 +1,14 @@
+"""
+Custom exceptions for pytest-mrt.
+
+Core logic raises these; framework layers (pytest fixture, CLI) catch and
+convert them to framework-appropriate errors (pytest.fail, typer.Exit).
+"""
+
+
+class MRTException(Exception):
+    """Base exception for all MRT errors."""
+
+
+class MRTConfigError(MRTException):
+    """Configuration validation error (missing file, invalid path, etc.)."""

pytest_mrt/plugin.py

@@ -10,6 +10,7 @@
 from .core.schema import SchemaSnapshot
 from .core.seeder import SmartSeeder
 from .core.verifier import RevisionResult, RollbackVerifier
+from .exceptions import MRTConfigError
 
 
 def _auto_detect_django(config: MRTConfig) -> MRTConfig:
@@ -80,7 +81,7 @@ def __init__(self, config: MRTConfig):
             from pathlib import Path as _Path
 
             if not _Path(config.alembic_ini).exists():
-                _hint = (
+                raise MRTConfigError(
                     f"\n\n  alembic.ini not found: '{config.alembic_ini}'\n\n"
                     "  If you are using Django migrations (not Alembic), use:\n\n"
                     "    config._mrt_config = MRTConfig(\n"
@@ -89,7 +90,6 @@ def __init__(self, config: MRTConfig):
                     "    )\n\n"
                     "  See: https://croc100.github.io/pytest-mrt/quickstart/#django"
                 )
-                pytest.fail(_hint, pytrace=False)
 
             self._runner = MigrationRunner(config.alembic_ini, config.db_url)
             self._seeder = SmartSeeder(self._runner.engine)
@@ -237,6 +237,9 @@ def pytest_configure(config: pytest.Config) -> None:
 @pytest.fixture
 def mrt(request: pytest.FixtureRequest) -> Iterator[MRTFixture]:
     cfg: MRTConfig = getattr(request.config, "_mrt_config", None) or MRTConfig()
-    fixture = MRTFixture(cfg)
+    try:
+        fixture = MRTFixture(cfg)
+    except MRTConfigError as e:
+        pytest.fail(str(e), pytrace=False)
     yield fixture
     fixture.reset()

tests/test_plugin.py

@@ -614,11 +614,13 @@ def test_auto_detect_django_no_switch_when_explicit_django_settings(tmp_path, mo
 # ── MRTFixture missing alembic.ini ─────────────────────────────────────
 
 def test_mrt_fixture_raises_on_missing_alembic_ini(tmp_path, monkeypatch):
-    """MRTFixture calls pytest.fail with a Django hint when alembic.ini is missing."""
+    """MRTFixture raises MRTConfigError with a Django hint when alembic.ini is missing."""
+    from pytest_mrt.exceptions import MRTConfigError
+
     monkeypatch.delenv("DJANGO_SETTINGS_MODULE", raising=False)
 
     cfg = MRTConfig(alembic_ini=str(tmp_path / "nonexistent.ini"), db_url="sqlite:///test.db")
-    with pytest.raises(pytest.fail.Exception, match="django_settings"):
+    with pytest.raises(MRTConfigError, match="django_settings"):
         MRTFixture(cfg)