add test

tests/test_standardize.py

@@ -2,6 +2,7 @@
 import numpy as np
 import pandas as pd
 import pandas.testing as tm
+import pytest
 
 import ibis_ml as ml
 
@@ -28,3 +29,14 @@ def test_scaleminmax():
     result = step.transform_table(table)
     expected = pd.DataFrame({"col": (cols - min_val) / (max_val - min_val)})
     tm.assert_frame_equal(result.execute(), expected, check_exact=False)
+
+
+@pytest.mark.parametrize("scaler", ["ScaleStandard", "ScaleMinMax"])
+def test_constant_columns(scaler):
+    table = ibis.memtable({"int_col": [100], "float_col": [100.0]})
+    scaler_class = getattr(ml, scaler)
+    scale_step = scaler_class(ml.numeric())
+    scale_step.fit_table(table, ml.core.Metadata())
+    result = scale_step.transform_table(table)
+    expected = pd.DataFrame({"int_col": [0.0], "float_col": [0.0]})
+    tm.assert_frame_equal(result.execute(), expected)