improvements of test coverage in fields

tests/fields/test_string_field.py

@@ -0,0 +1,43 @@
+import pytest
+
+from mongoengine import *
+from tests.utils import MongoDBTestCase, get_as_pymongo
+
+
+class TestStringField(MongoDBTestCase):
+    def test_storage(self):
+        class Person(Document):
+            name = StringField()
+
+        Person.drop_collection()
+        person = Person(name="test123")
+        person.save()
+        assert get_as_pymongo(person) == {"_id": person.id, "name": "test123"}
+
+    def test_validation(self):
+        class Person(Document):
+            name = StringField(max_length=20, min_length=2)
+            userid = StringField(r"[0-9a-z_]+$")
+
+        with pytest.raises(ValidationError, match="only accepts string values"):
+            Person(name=34).validate()
+
+        with pytest.raises(ValidationError, match="value is too short"):
+            Person(name="s").validate()
+
+        # Test regex validation on userid
+        person = Person(userid="test.User")
+        with pytest.raises(ValidationError):
+            person.validate()
+
+        person.userid = "test_user"
+        assert person.userid == "test_user"
+        person.validate()
+
+        # Test max length validation on name
+        person = Person(name="Name that is more than twenty characters")
+        with pytest.raises(ValidationError):
+            person.validate()
+
+        person = Person(name="a friendl name", userid="7a757668sqjdkqlsdkq")
+        person.validate()