✅ test: pytest gremlins

.github/workflows/ci.yml

@@ -89,10 +89,26 @@ jobs:
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
 
+  test_mutation:
+    name: Mutation Testing
+    runs-on: ubuntu-latest
+    needs: [format]
+    steps:
+      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@681c641aba71e4a1c380be3ab5e12ad51f415867 # v7.1.6
+
+      - name: Install
+        run: uv sync --no-default-groups --group nox --group test --locked
+
+      - name: Gremlins
+        run: uv run --frozen nox -s pytest_gremlins
+
   status:
     name: CI Pass
     runs-on: ubuntu-latest
-    needs: [format, tests, test_oldest]
+    needs: [format, tests, test_oldest, test_mutation]
     if: always()
     steps:
       - name: All required jobs passed

noxfile.py

@@ -22,9 +22,9 @@
 @session(uv_groups=["lint"], reuse_venv=True, default=True)
 def lint(s: nox.Session, /) -> None:
     """Run the linter."""
-    s.notify("precommit")
-    s.notify("pylint")
-    s.notify("mypy")
+    s.run("precommit")
+    s.run("pylint")
+    s.run("mypy")
 
 
 @session(uv_groups=["lint"], reuse_venv=True)
@@ -49,18 +49,27 @@ def mypy(s: nox.Session, /) -> None:
 # Testing
 
 
-@session(uv_groups=["test"], reuse_venv=True, default=True)
+@session(python=False, default=True)
 def test(s: nox.Session, /) -> None:
     """Run the unit and regular tests."""
     s.notify("pytest", posargs=s.posargs)
+    s.notify("pytest_gremlins", posargs=s.posargs)
 
 
-@session(uv_groups=["test"], reuse_venv=True)
+@session(uv_groups=["test_cov"], reuse_venv=True)
 def pytest(s: nox.Session, /) -> None:
     """Run the unit and regular tests."""
     s.run("pytest", *s.posargs)
 
 
+@session(uv_groups=["test_mutation"], reuse_venv=True)
+def pytest_gremlins(s: nox.Session, /) -> None:
+    """Run pytest-gremlins (without coverage, which conflicts with gremlins)."""
+    # Filter out --cov from posargs since it conflicts with gremlins
+    filtered_args = [arg for arg in s.posargs if not arg.startswith("--cov")]
+    s.run("pytest", "--gremlins", "tests", *filtered_args)
+
+
 # =============================================================================
 # Build
 

pyproject.toml

@@ -52,11 +52,12 @@ dev = [
 ]
 lint = ["mypy>=1.19.0", "pre-commit>=4.5.0", "pylint>=4.0.4"]
 nox = ["nox>=2024.10.9", "nox-uv>=0.6.3"]
-test = [
-  "attrs>=25.4.0",
-  "pytest>=8.4.2",
-  "pytest-cov>=7.0.0",
-  "sybil[pytest]>=9.2.0",
+test = ["pytest>=9.0.0", "sybil[pytest]>=9.2.0"]
+test_cov = [{ "include-group" = "test" }, "pytest-cov>=4.0.0", "attrs>=25.4.0"]
+test_mutation = [
+  { "include-group" = "test" },
+  "pytest-gremlins>=1.5.1",     # fails if `pytest-cov` is installed
+  "pytest-xdist>=3.8.0",
 ]
 
 [tool.hatch]