fix: show config errors once at session start instead of per-test

README.md

@@ -137,7 +137,7 @@ pip install pytest-mrt[oracle]   # python-oracledb
 pip install pytest-mrt[mssql]    # pymssql
 ```
 
-## Auto-fix missing reverse operations (v1.3.0)
+## Auto-fix missing reverse operations
 
 `mrt fix` generates missing reverse operations for both Alembic and Django migrations.
 
@@ -158,18 +158,29 @@ mrt clean-backups --db $DATABASE_URL
 mrt clean-backups --db $DATABASE_URL --label 0042_remove_user_phone --yes
 ```
 
-## pre-commit integration (v1.3.0)
+## pre-commit integration
 
 Add to `.pre-commit-config.yaml` to run `mrt check` automatically before every push:
 
 ```yaml
+# Alembic
 - repo: https://github.com/croc100/pytest-mrt
-  rev: v1.3.0
+  rev: v1.2.0
   hooks:
     - id: mrt-check
+      args: [alembic/versions/]
+
+# Django
+- repo: https://github.com/croc100/pytest-mrt
+  rev: v1.2.0
+  hooks:
+    - id: mrt-check
+      args: [myapp/migrations/]
 ```
 
-## Incremental CI — `--since` (v1.3.0)
+Update `rev` to the latest release tag. Run `pre-commit autoupdate` to keep it current.
+
+## Incremental CI — `--since`
 
 Check only migrations added since a given revision. Keeps CI fast on large codebases:
 
@@ -247,12 +258,13 @@ To suppress all MRT warnings on a line:
 
 Legacy syntax `# mrt: ignore` is still supported for backward compatibility.
 
-## What's new in v1.3.0
+## What's new in v1.2.0
 
-- **Django-aware `mrt fix`** — auto-generates reverse operations and data-safe backup/restore code for `RemoveField` and `DeleteModel`
-- **`mrt clean-backups`** — removes `_mrt_backups` rows after a deployment is confirmed stable
-- **`mrt check --since <revision>`** — incremental scan; only checks migrations added since a given git ref
-- **pre-commit hook** — add two lines to `.pre-commit-config.yaml` and `mrt check` runs automatically before every push
+- **MRT rule codes** (MRT101-MRT902) on all 44 patterns
+- **`# noqa: MRTxxx` suppression** — ruff/flake8-compatible per-line suppression syntax
+- **CLI refactored** into `commands/` subpackage
+- **`mrt check --since <revision>`** — incremental scan; only checks migrations added since a given revision
+- **pre-commit hook** — add to `.pre-commit-config.yaml` and `mrt check` runs automatically before every push
 
 ## Changelog
 

pytest_mrt/commands/init.py

@@ -17,28 +17,47 @@ def _detect_django_project() -> tuple[bool, str | None]:
     return False, None
 
 
+def _db_url_expr(db_url: str) -> str:
+    """Return db_url as a valid Python expression for conftest.py.
+
+    If the value looks like a Python expression (e.g. os.environ.get(...))
+    write it as-is. Otherwise wrap it in quotes so it becomes a string literal.
+    """
+    stripped = db_url.strip()
+    if stripped.startswith("os.") or stripped.startswith('"') or stripped.startswith("'"):
+        return stripped
+    return f'"{stripped}"'
+
+
 def _write_conftest(path: Path, alembic_ini: str, db_url: str) -> None:
+    url_expr = _db_url_expr(db_url)
+    needs_os = "os." in url_expr
+    imports = (
+        "import os\nfrom pytest_mrt import MRTConfig\n"
+        if needs_os
+        else "from pytest_mrt import MRTConfig\n"
+    )
     path.write_text(
-        f"import os\n"
-        f"from pytest_mrt import MRTConfig\n\n\n"
+        f"{imports}\n\n"
         f"def pytest_configure(config):\n"
         f"    config._mrt_config = MRTConfig(\n"
         f'        alembic_ini="{alembic_ini}",\n'
-        f"        db_url={db_url},\n"
-        f'        # skip={{"revision_id": "Reason this is a known issue"}},\n'
+        f"        db_url={url_expr},\n"
+        f'        # skip={{"revision_id": "Reason this migration is intentionally irreversible"}},\n'
         f"    )\n"
     )
 
 
 def _append_conftest(path: Path, alembic_ini: str, db_url: str) -> None:
+    url_expr = _db_url_expr(db_url)
     existing = path.read_text()
     addition = (
         f"\n\n# Added by mrt init\n"
         f"from pytest_mrt import MRTConfig\n\n\n"
         f"def pytest_configure(config):\n"
         f"    config._mrt_config = MRTConfig(\n"
         f'        alembic_ini="{alembic_ini}",\n'
-        f"        db_url={db_url},\n"
+        f"        db_url={url_expr},\n"
         f"    )\n"
     )
     path.write_text(existing + addition)
@@ -53,20 +72,30 @@ def _init_django(detected_settings: str | None) -> None:
         console.print("[yellow]Tip:[/yellow] Set DJANGO_SETTINGS_MODULE or provide it below.")
         settings = typer.prompt("Django settings module (e.g. myproject.settings_test)")
 
+    console.print(
+        "[dim]Tip: use sqlite:///test.db for local testing, "
+        "or set TEST_DATABASE_URL env var for CI.[/dim]"
+    )
     db_url = typer.prompt(
         "Test database URL",
-        default='os.environ.get("TEST_DATABASE_URL", "sqlite:///test.db")',
+        default="sqlite:///test.db",
     )
 
     test_dir = "tests" if Path("tests").exists() else "."
     conftest_path = Path(test_dir) / "conftest.py"
 
+    url_expr = _db_url_expr(db_url)
+    needs_os = "os." in url_expr
+    _imports = (
+        "import os\nfrom pytest_mrt import MRTConfig\n"
+        if needs_os
+        else "from pytest_mrt import MRTConfig\n"
+    )
     django_conftest = (
-        f"import os\n"
-        f"from pytest_mrt import MRTConfig\n\n\n"
+        f"{_imports}\n\n"
         f"def pytest_configure(config):\n"
         f"    config._mrt_config = MRTConfig(\n"
-        f"        db_url={db_url},\n"
+        f"        db_url={url_expr},\n"
         f'        django_settings="{settings}",\n'
         f'        # django_apps=["myapp", "otherapp"],  # restrict to specific apps\n'
         f"    )\n"
@@ -97,11 +126,16 @@ def _init_django(detected_settings: str | None) -> None:
         console.print(f"[green]✓[/green] Created [bold]{test_path}[/bold]")
 
     console.print()
-    console.print("[bold]Next steps:[/bold]")
-    console.print(f"  [cyan]pytest {test_dir}/test_migrations.py -s[/cyan]")
+    console.print("[bold]Setup complete. Next steps:[/bold]")
+    console.print()
+    console.print("  1. Run dynamic rollback tests (requires a test DB):")
+    console.print(f"     [cyan]pytest {test_dir}/test_migrations.py -s[/cyan]")
     console.print()
-    console.print("[dim]Static analysis (no DB needed):[/dim]")
-    console.print("  [cyan]mrt check yourapp/migrations/[/cyan]")
+    console.print("  2. Run static analysis (no DB needed):")
+    console.print("     [cyan]mrt check yourapp/migrations/[/cyan]")
+    console.print()
+    console.print("  [dim]If tests fail, run with -v for details or check docs:[/dim]")
+    console.print("  [dim]https://croc100.github.io/pytest-mrt[/dim]")
 
 
 def init() -> None:
@@ -124,9 +158,13 @@ def init() -> None:
     else:
         found_ini = typer.prompt("Path to alembic.ini", default="alembic.ini")
 
+    console.print(
+        "[dim]Tip: use sqlite:///test.db for local testing, "
+        "or set TEST_DATABASE_URL env var for CI.[/dim]"
+    )
     db_url = typer.prompt(
         "Test database URL",
-        default='os.environ.get("TEST_DATABASE_URL", "sqlite:///test.db")',
+        default="sqlite:///test.db",
     )
 
     test_dir = "tests" if Path("tests").exists() else "."
@@ -153,5 +191,13 @@ def init() -> None:
         console.print(f"[green]✓[/green] Created [bold]{test_path}[/bold]")
 
     console.print()
-    console.print("[bold]Next steps:[/bold]")
-    console.print(f"  [cyan]pytest {test_dir}/test_migrations.py -s[/cyan]")
+    console.print("[bold]Setup complete. Next steps:[/bold]")
+    console.print()
+    console.print("  1. Run dynamic rollback tests (requires a test DB):")
+    console.print(f"     [cyan]pytest {test_dir}/test_migrations.py -s[/cyan]")
+    console.print()
+    console.print("  2. Run static analysis (no DB needed):")
+    console.print(f"     [cyan]mrt check {found_ini.replace('alembic.ini', 'versions/')}[/cyan]")
+    console.print()
+    console.print("  [dim]If tests fail, run with -v for details or check docs:[/dim]")
+    console.print("  [dim]https://croc100.github.io/pytest-mrt[/dim]")

pytest_mrt/plugin.py

@@ -83,13 +83,9 @@ def __init__(self, config: MRTConfig):
 
             if not _Path(config.alembic_ini).exists():
                 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"
-                    "        db_url=os.environ['TEST_DATABASE_URL'],\n"
-                    "        django_settings='myproject.settings_test',\n"
-                    "    )\n\n"
-                    "  See: https://croc100.github.io/pytest-mrt/quickstart/#django"
+                    f"alembic.ini not found: '{config.alembic_ini}'\n\n"
+                    "Check the path and update MRTConfig(alembic_ini=...) in your conftest.py.\n"
+                    "See: https://croc100.github.io/pytest-mrt/quickstart/"
                 )
 
             self._runner = MigrationRunner(config.alembic_ini, config.db_url)
@@ -301,6 +297,39 @@ def pytest_configure(config: pytest.Config) -> None:
     config.addinivalue_line("markers", "mrt: migration rollback test")
 
 
+def pytest_sessionstart(session: pytest.Session) -> None:
+    """Validate MRTConfig once at session start.
+
+    Catches obvious setup errors (missing alembic.ini, etc.) before any test
+    runs, so the user sees one clear error instead of the same message repeated
+    for every collected test.
+    """
+    cfg: MRTConfig | None = getattr(session.config, "_mrt_config", None)
+    if cfg is None:
+        return
+
+    cfg = _auto_detect_django(cfg)
+
+    # Django mode — no alembic.ini needed
+    if cfg.django_settings is not None:
+        return
+
+    from pathlib import Path
+
+    if not Path(cfg.alembic_ini).exists():
+        msg = (
+            f"alembic.ini not found: '{cfg.alembic_ini}'\n\n"
+            "Check the path and update MRTConfig(alembic_ini=...) in your conftest.py.\n\n"
+            "If you are using Django migrations (not Alembic), set django_settings instead:\n\n"
+            "    config._mrt_config = MRTConfig(\n"
+            "        db_url=os.environ['TEST_DATABASE_URL'],\n"
+            "        django_settings='myproject.settings_test',\n"
+            "    )\n\n"
+            "See: https://croc100.github.io/pytest-mrt/quickstart/"
+        )
+        pytest.exit(msg, returncode=4)
+
+
 def pytest_collection_modifyitems(
     session: pytest.Session,
     config: pytest.Config,
@@ -336,9 +365,15 @@ def pytest_collection_modifyitems(
 @pytest.fixture
 def mrt(request: pytest.FixtureRequest) -> Iterator[MRTFixture]:
     cfg: MRTConfig = getattr(request.config, "_mrt_config", None) or MRTConfig()
+    # Capture error outside the except block to avoid "During handling of the
+    # above exception, another exception occurred" in the traceback output.
+    config_error: str | None = None
     try:
         fixture = MRTFixture(cfg)
     except MRTConfigError as e:
-        pytest.fail(str(e), pytrace=False)
+        config_error = str(e)
+    if config_error is not None:
+        pytest.fail(config_error, pytrace=False)
+        return  # unreachable; keeps type checkers happy
     yield fixture
     fixture.reset()

tests/test_plugin.py

@@ -665,13 +665,13 @@ def test_auto_detect_django_no_switch_when_explicit_django_settings(tmp_path, mo
 
 
 def test_mrt_fixture_raises_on_missing_alembic_ini(tmp_path, monkeypatch):
-    """MRTFixture raises MRTConfigError with a Django hint when alembic.ini is missing."""
+    """MRTFixture raises MRTConfigError 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(MRTConfigError, match="django_settings"):
+    with pytest.raises(MRTConfigError, match="alembic.ini not found"):
         MRTFixture(cfg)