--- a
+++ b/tests/preprocessing/test_summarize_measurements.py
@@ -0,0 +1,51 @@
+import numpy as np
+import pytest
+from anndata import AnnData
+from pandas import DataFrame
+
+from ehrapy.preprocessing import summarize_measurements
+
+
+@pytest.fixture
+def adata_to_expand(rng):
+    row_ids = ["pat1", "pat1", "pat1", "pat2", "pat2", "pat3"]
+    measurement1 = rng.choice([0, 1], size=6)
+    measurement2 = rng.uniform(0, 20, size=6)
+    measurement3 = rng.uniform(0, 20, size=6)
+    data_dict = {"measurement1": measurement1, "measurement2": measurement2, "measurement3": measurement3}
+    data_df = DataFrame(data_dict, index=row_ids)
+    adata = AnnData(X=data_df)
+
+    return adata
+
+
+def test_all_statistics(adata_to_expand):
+    transformed_adata = summarize_measurements(
+        adata_to_expand,
+    )
+
+    assert transformed_adata.shape == (3, 9)  # (3 patients, 3 measurements * 3 statistics)
+    assert np.allclose(
+        transformed_adata[:, "measurement2_min"].X.reshape(-1), np.array([1.883547, 15.222794, 2.5622725])
+    )
+    assert np.allclose(
+        transformed_adata[:, "measurement2_max"].X.reshape(-1), np.array([19.512447, 15.721286, 2.5622725])
+    )
+    assert np.allclose(
+        transformed_adata[:, "measurement2_mean"].X.reshape(-1), np.array([11.781118, 15.47204, 2.5622725])
+    )
+
+
+def test_var_names_subset(adata_to_expand):
+    transformed_adata = summarize_measurements(
+        adata_to_expand,
+        var_names=["measurement1", "measurement2"],
+    )
+
+    assert transformed_adata.shape == (3, 6)  # (3 patients, 2 measurements * 3 statistics)
+
+
+def test_statistics_subset(adata_to_expand):
+    transformed_adata = summarize_measurements(adata_to_expand, statistics=["min"])
+
+    assert transformed_adata.shape == (3, 3)  # (3 patients, 3 measurements * 1 statistics)