Changes according to comments

Author: kotamatsuoka

pandas/core/internals/construction.py

@@ -242,7 +242,7 @@ def init_dict(data, index, columns, dtype=None):
 
         # no obvious "empty" int column
         if missing.any() and not is_integer_dtype(dtype):
-            if is_dtype_equal(dtype, "string"):
+            if is_extension_array_dtype(dtype):
                 # GH 33623
                 nan_dtype = dtype
             elif dtype is None or np.issubdtype(dtype, np.flexible):

pandas/tests/extension/test_common.py

@@ -79,3 +79,9 @@ def test_astype_no_copy():
 def test_is_extension_array_dtype(dtype):
     assert isinstance(dtype, dtypes.ExtensionDtype)
     assert is_extension_array_dtype(dtype)
+
+
+@pytest.mark.parametrize("columns, dtype", [(["a"], "string")])
+def test_construct_empty_dataframe_with_string_dtype(columns, dtype):
+    # GH 33623
+    pd.DataFrame(columns=columns, dtype=dtype)

pandas/tests/frame/test_constructors.py

@@ -2679,7 +2679,3 @@ def test_construction_from_set_raises(self):
         msg = "Set type is unordered"
         with pytest.raises(TypeError, match=msg):
             pd.DataFrame({"a": {1, 2, 3}})
-
-    def test_construct_empty_dataframe_with_string_dtype(self):
-        # GH 33623
-        pd.DataFrame(columns=["a"], dtype="string")