diff --git a/tests/test_preprocessing.py b/tests/test_preprocessing.py
index 332c39b6..f2ad7a5f 100644
--- a/tests/test_preprocessing.py
+++ b/tests/test_preprocessing.py
@@ -16,11 +16,11 @@
 df = pd.DataFrame(np.random.randn(N_PTS, len(cols)), columns=cols)
 
 def square(df,col):
-    df[f'col_squared'] = df[col] ** 2
+    df[f'{col}_squared'] = df[col] ** 2
     return df
 
 def add(df,col,value):
-    df[f'col_added'] = df[col] + value
+    df[f'{col}_added'] = df[col] + value
     return df
 
 def test_pp_decorator():