--- a
+++ b/tests/preprocessing/test_outliers.py
@@ -0,0 +1,37 @@
+import numpy as np
+
+import ehrapy as ep
+
+
+def test_winsorize_var(mimic_2_10):
+    winsorized_adata = ep.pp.winsorize(mimic_2_10, vars=["age"], limits=[0.2, 0.2], copy=True)
+    expected = np.array(
+        [71.43198, 64.92076, 36.5, 44.49191, 25.41667, 36.54657, 25.41667, 71.43198, 71.43198, 25.41667]
+    ).reshape((10, 1))
+
+    np.testing.assert_allclose(np.array(winsorized_adata[:, "age"].X, dtype=np.float32), expected)
+
+
+def test_winsorized_obs(mimic_2_10):
+    to_winsorize_obs = ep.ad.move_to_obs(mimic_2_10, "age")
+    winsorized_adata = ep.pp.winsorize(to_winsorize_obs, obs_cols=["age"], limits=[0.2, 0.2], copy=True)
+    expected = np.array(
+        [71.43198, 64.92076, 36.5, 44.49191, 25.41667, 36.54657, 25.41667, 71.43198, 71.43198, 25.41667]
+    )
+
+    np.testing.assert_allclose(np.array(winsorized_adata.obs["age"]), expected)
+
+
+def test_clip_var(mimic_2_10):
+    clipped_adata = ep.pp.clip_quantile(mimic_2_10, vars=["age"], limits=(25, 50), copy=True)
+    expected = np.array([50, 50, 36.5, 44.49191, 25, 36.54657, 25, 50, 50, 25.41667]).reshape((10, 1))
+
+    np.testing.assert_allclose(np.array(clipped_adata[:, "age"].X, dtype=np.float32), expected)
+
+
+def test_clip_obs(mimic_2_10):
+    to_clip_obs = ep.ad.move_to_obs(mimic_2_10, "age")
+    clipped_adata = ep.pp.clip_quantile(to_clip_obs, obs_cols=["age"], limits=(25, 50), copy=True)
+    expected = np.array([50, 50, 36.5, 44.49191, 25, 36.54657, 25, 50, 50, 25.41667])
+
+    np.testing.assert_allclose(np.array(clipped_adata.obs["age"]), expected)