test: add workflow to test PRs (#36)

Author: jradcliff

.github/workflows/presubmit.yaml

@@ -0,0 +1,28 @@
+# Runs tests on pull requests for main
+permissions: read-all
+name: Presubmit
+on:
+  pull_request:
+    branches:
+      - main
+jobs:
+  test:
+    strategy:
+      matrix:
+        python-version: ["3.10", "3.11", "3.12", "3.13"]
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Set up Python
+      uses: actions/setup-python@v5
+      with:
+        python-version: ${{ matrix.python-version }}
+        cache: 'pip'
+
+    - name: Install nox
+      run: pip install -e .[dev]
+
+    - name: Check formatting
+      run: nox -s lint
+    - name: Run tests
+      run: nox -s tests-${{ matrix.python-version }}

noxfile.py

@@ -38,17 +38,42 @@
 ]
 
 
+def _format(session, check=False):
+    """Helper function to run formatters.
+
+    Args:
+      session: The nox session object.
+      check: If True, checks formatting and fails if any file requires
+        formatting, but doesn't apply any changes. If False, applies formatting
+        fixes.
+    """
+    black_command = ["black"]
+    if check:
+        black_command.append("--check")
+
+    black_command.extend(
+        [
+            "-l",
+            "80",
+            "--exclude",
+            r"/(v[0-9]+|\.eggs|\.git|_cache|\.nox|\.tox|\.venv|env|venv|\.svn|_build|buck-out|build|dist)/",
+            ".",
+        ]
+    )
+
+    session.run(*black_command)
+
+
+@nox.session(venv_backend="none")
+def lint(session):
+    """Fails if the code is not formatted correctly."""
+    _format(session, check=True)
+
+
 @nox.session(venv_backend="none")
 def format(session):
     """Runs the black formatter and applies formatting fixes."""
-    session.run(
-        "black",
-        "-l",
-        "80",
-        "--exclude",
-        r"/(v[0-9]+|\.eggs|\.git|_cache|\.nox|\.tox|\.venv|env|venv|\.svn|_build|buck-out|build|dist)/",
-        ".",
-    )
+    _format(session)
 
 
 @nox.session(python=PYTHON_VERSIONS)