TST: added unitest for read_excel and modified series/test_dtypes for np.nan to empty string (pandas-dev#20377)

Author: nikoskaragiannakis

pandas/tests/io/test_excel.py

@@ -361,6 +361,35 @@ def test_reader_dtype(self, ext):
         with pytest.raises(ValueError):
             actual = self.get_exceldf(basename, ext, dtype={'d': 'int64'})
 
+    def test_reader_dtype_str(self, ext):
+        # GH 20377
+        basename = 'testdtype'
+        actual = self.get_exceldf(basename, ext)
+
+        expected = DataFrame({
+            'a': [1, 2, 3, 4],
+            'b': [2.5, 3.5, 4.5, 5.5],
+            'c': [1, 2, 3, 4],
+            'd': [1.0, 2.0, np.nan, 4.0]}).reindex(
+                columns=['a', 'b', 'c', 'd'])
+
+        tm.assert_frame_equal(actual, expected)
+
+        actual = self.get_exceldf(basename, ext,
+                                  dtype={'a': 'float64',
+                                         'b': 'float32',
+                                         'c': str,
+                                         'd': str})
+
+        expected['a'] = expected['a'].astype('float64')
+        expected['b'] = expected['b'].astype('float32')
+        expected['c'] = ['001', '002', '003', '004']
+        expected['d'] = ['1', '2', '', '4']
+        tm.assert_frame_equal(actual, expected)
+
+        with pytest.raises(ValueError):
+            actual = self.get_exceldf(basename, ext, dtype={'d': 'int64'})
+
     def test_reading_all_sheets(self, ext):
         # Test reading all sheetnames by setting sheetname to None,
         # Ensure a dict is returned.

pandas/tests/series/test_dtypes.py

@@ -142,7 +142,7 @@ def test_astype_datetime64tz(self):
                                                 tm.rands(1000)]),
                                         Series([string.digits * 10,
                                                 tm.rands(63),
-                                                tm.rands(64), nan, 1.0])])
+                                                tm.rands(64), '', 1.0])])
     def test_astype_str_map(self, dtype, series):
         # see gh-4405
         result = series.astype(dtype)