TST: added unitest for read_csv (pandas-dev#20377)

Author: nikoskaragiannakis

pandas/tests/series/test_io.py

@@ -162,6 +162,16 @@ def test_to_csv_compression(self, compression_no_zip):
                                                    index_col=0,
                                                    squeeze=True))
 
+    def test_from_csv_dtype_str(self):
+        # GH20377
+        s = Series([1, 2, np.nan, 4], index=['A', 'B', 'C', 'D'],
+                   name='X')
+        with ensure_clean() as filename:
+            s.to_csv(filename, header=True)
+            rs = pd.read_csv(filename, dtype=str)
+            expected = Series(['1.0', '2.0', '', '4.0'], name=s.name)
+            assert_series_equal(rs.X, expected)
+
 
 class TestSeriesIO(TestData):