add test for read_csv nrow=0 and low_memory=True, issue 21141

Author: r00ta

pandas/tests/io/parser/common.py

@@ -16,7 +16,7 @@
 
 import pandas as pd
 import pandas.util.testing as tm
-from pandas import DataFrame, Series, Index, MultiIndex
+from pandas import DataFrame, Series, Index, MultiIndex, Int64Index
 from pandas import compat
 from pandas.compat import (StringIO, BytesIO, PY3,
                            range, lrange, u)
@@ -238,6 +238,16 @@ def test_csv_mixed_type(self):
         out = self.read_csv(StringIO(data))
         tm.assert_frame_equal(out, expected)
 
+    def test_csv_index_col_and_nrows(self):
+        data = """A,B,C
+1,1,1,2
+2,2,3,4
+3,3,4,5
+"""
+        out = self.read_csv(StringIO(data), low_memory=True, index_col=0, nrows=0)
+        tm.assert_index_equal(out.columns, pd.Index(['A', 'B', 'C']))
+        assert out.empty
+
     def test_read_csv_dataframe(self):
         df = self.read_csv(self.csv1, index_col=0, parse_dates=True)
         df2 = self.read_table(self.csv1, sep=',', index_col=0,