diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 713583b..341a579 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -28,19 +28,19 @@ jobs:
           python: '3.9'
           nox_session: tests-3.9
 
-        - name: Tests, Python 3.11, macOS
+        - name: Tests, Python 3.11, with code coverage, macOS
           os: macos-latest
           python: '3.11'
-          nox_session: tests-3.11
+          nox_session: tests-3.11(cov)
 
         - name: Tests, Python 3.10, macOS
           os: macos-latest
           python: '3.9'
           nox_session: tests-3.9
 
-        - name: Documentation, Python 3.12, Ubuntu
+        - name: Documentation, Python 3.11, Ubuntu
           os: ubuntu-latest
-          python: '3.12'
+          python: '3.11'
           nox_session: docs
 
     steps:
@@ -67,10 +67,12 @@ jobs:
         run: python -m pip install --progress-bar off --upgrade nox
 
       - name: Run tests
-        run: nox -s ${{ matrix.nox_session }}
+        run: nox -s '${{ matrix.nox_session }}'
 
       - name: Upload coverage to codecov
         if: ${{ contains(matrix.nox_session,'cov') }}
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v4
         with:
           file: ./coverage.xml
+        env:
+          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
diff --git a/codecov.yml b/codecov.yml
new file mode 100644
index 0000000..930d53f
--- /dev/null
+++ b/codecov.yml
@@ -0,0 +1,16 @@
+codecov:
+  notify:
+    wait_for_ci: false
+  require_ci_to_pass: false
+# coverage:
+#   range: 90..98
+#   status:
+#     project:
+#       default:
+#         # Temporarily allow a greater project coverage threshold; see #2757
+#         threshold: 0.9%
+#         removed_code_behavior: adjust_base
+#     patch:
+#       default:
+#         threshold: 0.5%
+#         removed_code_behavior: adjust_base
diff --git a/mamba_environment.yml b/mamba_environment.yml
index 901e5ce..06489b1 100644
--- a/mamba_environment.yml
+++ b/mamba_environment.yml
@@ -6,7 +6,7 @@ channels:
 dependencies:
   - python
   - jupyter
-  - numpy
+  - numpy < 2
   - scipy
   - matplotlib
   - mdsplus
@@ -16,5 +16,6 @@ dependencies:
   - sphinx
   - pip
   - pip:
-    - pytest
     - nox
+    - pytest
+    - pytest-cov
diff --git a/noxfile.py b/noxfile.py
index 0c6aafc..8668288 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -23,13 +23,42 @@ def install_environment(session, environment_path="mamba_environment.yml"):
         ],
         silent=False,
     )
+    session.run(
+        *[
+            session.venv_backend,
+            "list",
+            "--prefix",
+            session.virtualenv.location,
+        ]
+    )
+
+
+test_specifiers: list = [
+    nox.param("run all tests", id="all"),
+    nox.param("with code coverage", id="cov"),
+]
+
+with_coverage: tuple[str, ...] = (
+    "--cov=wipplpy",
+    "--cov-report=xml",
+    "--cov-config=pyproject.toml",
+    "--cov-append",
+    "--cov-report",
+    "xml:coverage.xml",
+)
 
 
 @nox.session(python=supported_python_versions)
-def tests(session):
+@nox.parametrize("test_specifier", test_specifiers)
+def tests(session, test_specifier):
     """Run tests with pytest."""
     install_environment(session)
-    session.run("pytest")
+
+    options = []
+    if test_specifier == "with code coverage":
+        options += with_coverage
+
+    session.run("pytest", *options)
 
 
 @nox.session(python=maxpython)