diff --git a/ensemble_md/tests/test_analyze_free_energy.py b/ensemble_md/tests/test_analyze_free_energy.py
index e674d7ac..dc88fe74 100644
--- a/ensemble_md/tests/test_analyze_free_energy.py
+++ b/ensemble_md/tests/test_analyze_free_energy.py
@@ -188,6 +188,7 @@ def test_combine_df_adjacent():
     state_ranges = [[0, 1, 2], [1, 2, 3]]
 
     # Test 1: df_err_adjacent is None (in which case err_type is ignored)
+    # Note that this test would lead to two harmless RuntimWarnings due to calculations like np.std([1], ddof=1), which return NaN  # noqa: E501
     results = analyze_free_energy._combine_df_adjacent(df_adjacent, state_ranges, None, "propagate")
     assert results[0] == [1, 3.5, 6]
     assert math.isnan(results[1][0])
diff --git a/ensemble_md/tests/test_analyze_traj.py b/ensemble_md/tests/test_analyze_traj.py
index e3135707..b47b3fd9 100644
--- a/ensemble_md/tests/test_analyze_traj.py
+++ b/ensemble_md/tests/test_analyze_traj.py
@@ -291,6 +291,7 @@ def test_traj2transmtx():
     np.testing.assert_array_equal(analyze_traj.traj2transmtx(traj, N, normalize=False), array)
 
     # Case 2: normalize=True
+    # This test would lead to a harmless RuntimeWarnings due to 0/0 in the last row.
     array = np.array([
         [0, 0.5, 0, 0.5],
         [0.5, 0, 0.5, 0],