test: Use NaN for missing matches

tests/test_api.py

@@ -1,5 +1,6 @@
 import bdikit as bdi
 import pandas as pd
+import numpy as np
 from bdikit.mapping_algorithms.value_mapping.value_mappers import (
     FunctionValueMapper,
     IdentityValueMapper,
@@ -205,7 +206,7 @@ def test_end_to_end_api_integration():
     assert len(column_mappings.index) == 1
 
     # when: pass output of match_schema() directly to materialize_mapping(),
-    # the column must be ranamed to the target column without any value mapping
+    # the column must be renamed to the target column without any value mapping
     df_mapped = bdi.materialize_mapping(df_source, column_mappings)
     # then
     assert "tgt_column" in df_mapped.columns
@@ -237,17 +238,18 @@ def test_end_to_end_api_integration():
     # matching values found during the value matching step
     assert isinstance(df_mapped, pd.DataFrame)
     assert "tgt_column" in df_mapped.columns
-    assert df_mapped["tgt_column"].tolist() == ["apple", "banana", "orange", None]
+    assert df_mapped["tgt_column"].tolist() == ["apple", "banana", "orange", np.nan]
 
     # when: pass output of match_values() to merge_mappings() and then to
     # materialize_mapping()
+
     harmonization_spec = bdi.merge_mappings(value_mappings, [])
     df_mapped = bdi.materialize_mapping(df_source, harmonization_spec)
 
-    # then: the column must be ranamed and values must be mapped
+    # then: the column must be renamed and values must be mapped
     assert isinstance(df_mapped, pd.DataFrame)
     assert "tgt_column" in df_mapped.columns
-    assert df_mapped["tgt_column"].tolist() == ["apple", "banana", "orange", None]
+    assert df_mapped["tgt_column"].tolist() == ["apple", "banana", "orange", np.nan]
 
     # when: user mappings are specified in merge_mappings()
     user_mappings = [
@@ -264,10 +266,10 @@ def test_end_to_end_api_integration():
     harmonization_spec = bdi.merge_mappings(value_mappings, user_mappings)
     df_mapped = bdi.materialize_mapping(df_source, harmonization_spec)
 
-    # then: user mappings take precedence, so the column must be ranamed and
+    # then: user mappings take precedence, so the column must be renamed and
     # values must be mapped according the provide user_mappings
     assert "tgt_column" in df_mapped.columns
-    assert df_mapped["tgt_column"].tolist() == ["APPLE", "BANANA", "ORANGE", None]
+    assert df_mapped["tgt_column"].tolist() == ["APPLE", "BANANA", "ORANGE", np.nan]
 
 
 def test_top_matches_and_match_values_integration():