Add test cases with 1 and 3 columns

Author: syxolk

pandas/tests/io/formats/test_to_latex.py

@@ -378,6 +378,14 @@ def test_to_latex_longtable(self, frame):
 
         assert withoutindex_result == withoutindex_expected
 
+        df = DataFrame({'a': [1, 2]})
+        with1column_result = df.to_latex(index=False, longtable=True)
+        assert "\multicolumn{1}" in with1column_result
+
+        df = DataFrame({'a': [1, 2], 'b': [3, 4], 'c': [5, 6]})
+        with3columns_result = df.to_latex(index=False, longtable=True)
+        assert "\multicolumn{3}" in with3columns_result
+
     def test_to_latex_escape_special_chars(self):
         special_characters = ['&', '%', '$', '#', '_', '{', '}', '~', '^',
                               '\\']