3rd review changes

firestore/google/cloud/firestore_v1beta1/_helpers.py

@@ -127,8 +127,9 @@ class FieldPath(object):
 
     def __init__(self, *parts):
         for part in parts:
-            if not isinstance(part, six.string_types):
-                raise ValueError("One or more components is not a string.")
+            if not isinstance(part, six.string_types) or not part:
+                error = 'One or more components is not a string or is empty.'
+                raise ValueError(error)
         self.parts = tuple(parts)
 
     @staticmethod
@@ -146,10 +147,10 @@ def from_string(string):
             as arguments to `FieldPath`.
         """
         invalid_characters = '~*/[]'
+        for invalid_character in invalid_characters:
+            if invalid_character in string:
+                raise ValueError('Invalid characters in string.')
         string = string.split('.')
-        for part in string:
-            if not part or part in invalid_characters:
-                raise ValueError("No string or invalid characters in string.")
         return FieldPath(*string)
 
     def to_api_repr(self):

firestore/tests/unit/test__helpers.py

@@ -102,6 +102,10 @@ def test_none_fails(self):
         with self.assertRaises(ValueError):
             field_path = self._make_one('a', None, 'b')
 
+    def test_empty_string_in_part_fails(self):
+        with self.assertRaises(ValueError):
+            field_path = self._make_one('a', '', 'b')
+
     def test_integer_fails(self):
         with self.assertRaises(ValueError):
             field_path = self._make_one('a', 3, 'b')
@@ -210,15 +214,15 @@ def test_tuple_fails(self):
             field_path = self._make_one(parts)
 
     def test_equality(self):
-        field_path = self._make_one("a", "b")
-        string_path = self._get_target_class().from_string("a.b")
+        field_path = self._make_one('a', 'b')
+        string_path = self._get_target_class().from_string('a.b')
         self.assertEqual(field_path, string_path)
 
     def test_non_equal_types(self):
         import mock
         mock = mock.Mock()
-        mock.parts = "a", "b"
-        field_path = self._make_one("a", "b")
+        mock.parts = 'a', 'b'
+        field_path = self._make_one('a', 'b')
         self.assertNotEqual(field_path, mock)
 
     def test_key(self):