diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 0000000..bcc6cd7
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,52 @@
+name: Test
+
+on:
+  push:
+  pull_request:
+  schedule:
+    - cron: '52 4 3 * *'  # 4:52a on third day of the month
+
+concurrency:
+  group: ${{ github.ref }}-${{ github.workflow }}
+  cancel-in-progress: true
+
+jobs:
+
+  test:
+    name: Run tests
+    if:
+      github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository
+
+    runs-on: ${{ matrix.os }}
+
+    defaults:
+      run:
+        shell: bash -l {0}
+
+    strategy:
+      matrix:
+        os: [ubuntu-latest]
+        python-version: ["3.14"]
+
+    steps:
+      - uses: actions/checkout@v7
+
+      - name: Install Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v7
+        with:
+          python-version: ${{ matrix.python-version }}
+
+      - name: Install package and dependencies
+        run: pip install .[testing]
+
+      - name: Check example script
+        run: |
+          python -m diffusion_model > model.out
+
+      - name: Check example notebook
+        run: |
+          pytest notebooks --nbmake --nbmake-timeout=3000 --nbmake-kernel=python3 -v
+
+      - name: Run unit tests
+        run: |
+          pytest -v
diff --git a/pyproject.toml b/pyproject.toml
index 50243e2..a070fc8 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -14,5 +14,11 @@ dependencies = [
     "numpy",
 ]
 
+[project.optional-dependencies]
+testing = [
+  "pytest",
+  "nbmake",
+]
+
 [tool.setuptools]
 py-modules = ["diffusion_model"]
diff --git a/tests/test_diffusion_model.py b/tests/test_diffusion_model.py
index c0cbffc..2462d90 100644
--- a/tests/test_diffusion_model.py
+++ b/tests/test_diffusion_model.py
@@ -36,10 +36,10 @@ def test_time_step_decreases_with_diffusivity():
 def test_step_like_is_array_of_float():
     """Check profile is a numpy array of floats."""
     z = step_like([1.0, 2.0, 3.0])
-    return isinstance(z, np.ndarray) and np.issubdtype(z.dtype, np.floating)
+    assert isinstance(z, np.ndarray) and np.issubdtype(z.dtype, np.floating)
 
     z = step_like([1, 2, 3])
-    return isinstance(z, np.ndarray) and np.issubdtype(z.dtype, np.floating)
+    assert isinstance(z, np.ndarray) and np.issubdtype(z.dtype, np.floating)
 
 
 def test_step_like_length():