NHSDigital
diff --git a/‎codonPython/tests/check_null_test.py‎
Lines changed: 32 additions & 0 deletions b/‎codonPython/tests/check_null_test.py‎
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+from codonPython.check_null import check_null
+import numpy as np
+import pandas as pd
+import pytest
+
+testdata = pd.DataFrame({
+    "col1" : [1,2,3,4,5,6,7,8,9,10],
+    "col2" : [11,12,13,14,15,np.nan,np.nan,18,19,20],
+})
+
+@pytest.mark.parametrize("dataframe, columns_to_be_checked, expected", [
+    (testdata.iloc[:5, :], ["col1", "col2"], 0),
+    (testdata, ["col2"], 2),
+])
+def test_BAU(dataframe, columns_to_be_checked, expected):
+    assert check_null(dataframe, columns_to_be_checked) == expected
+
+
+@pytest.mark.parametrize("dataframe, columns_to_be_checked", [
+    (testdata, 0.01),
+])
+def test_ValueError(dataframe, columns_to_be_checked):
+    with pytest.raises(ValueError):
+        check_null(dataframe, columns_to_be_checked)
+
+
+@pytest.mark.parametrize("dataframe, columns_to_be_checked", [
+    (testdata, ["wrong_column"]),
+])
+def test_KeyError(dataframe, columns_to_be_checked):
+    with pytest.raises(KeyError):
+        check_null(dataframe, columns_to_be_checked)