Add a test covering basic Document operations

It covers operations such as:
1. Document initialization.
2. Accessing/setting attributes on a Document instance.
3. Serializing a Document instance (via `to_mongo`).
4. Deserializing a Document instance (via `_from_son`).
5. Serializing + saving a Document in the database (via `save`).
5. Loading a Document from the database + deserializing (via `Doc.objects[0]`).

And it does so for both basic flat documents and more complex nested docs.

benchmarks/test_basic_doc_ops.py

@@ -0,0 +1,112 @@
+import unittest
+from timeit import repeat
+
+import mongoengine
+from mongoengine import (BooleanField, Document, EmbeddedDocument,
+                         EmbeddedDocumentField, IntField, ListField,
+                         StringField)
+
+conn_settings = {
+    'db': 'mongoengine-benchmark-test',
+}
+
+mongoengine.connect(**conn_settings)
+
+
+def timeit(f, n=10000):
+    return min(repeat(f, repeat=3, number=n)) / float(n)
+
+
+def test_basic():
+    class Book(Document):
+        name = StringField()
+        pages = IntField()
+        tags = ListField(StringField())
+        is_published = BooleanField()
+
+    Book.drop_collection()
+
+    def init_book():
+        return Book(
+            name='Always be closing',
+            pages=100,
+            tags=['self-help', 'sales'],
+            is_published=True,
+        )
+
+    print 'Doc initialization: %.3fus' % (timeit(init_book, 1000) * 10**6)
+
+    b = init_book()
+    print 'Doc getattr: %.3fus' % (timeit(lambda: b.name, 10000) * 10**6)
+
+    print 'Doc setattr: %.3fus' % (
+        timeit(lambda: setattr(b, 'name', 'New name'), 10000) * 10**6
+    )
+
+    print 'Doc to mongo: %.3fus' % (timeit(b.to_mongo, 1000) * 10**6)
+
+    def save_book():
+        b._mark_as_changed('name')
+        b._mark_as_changed('tags')
+        b.save()
+
+    save_book()
+    son = b.to_mongo()
+
+    print 'Load from SON: %.3fus' % (
+        timeit(lambda: Book._from_son(son), 1000) * 10**6
+    )
+
+    print 'Save to database: %.3fus' % (timeit(save_book, 100) * 10**6)
+
+    print 'Load from database: %.3fus' % (
+        timeit(lambda: Book.objects[0], 100) * 10**6
+    )
+
+
+def test_embedded():
+    class Contact(EmbeddedDocument):
+        name = StringField()
+        title = StringField()
+        address = StringField()
+
+    class Company(Document):
+        name = StringField()
+        contacts = ListField(EmbeddedDocumentField(Contact))
+
+    Company.drop_collection()
+
+    def init_company():
+        return Company(
+            name='MongoDB, Inc.',
+            contacts=[
+                Contact(
+                    name='Contact %d' % x,
+                    title='CEO',
+                    address='Address %d' % x,
+                )
+                for x in range(1000)
+            ]
+        )
+
+    def create_company():
+        c = init_company()
+        c.save()
+        c.delete()
+
+    print 'Save/delete big object to database: %.3fms' % (
+        timeit(create_company, 10) * 10**3
+    )
+
+    c = init_company().save()
+    print 'Serialize big object: %.3fms' % (
+        timeit(c.to_mongo, 100) * 10**3
+    )
+    print 'Load big object from database: %.3fms' % (
+        timeit(lambda: Company.objects[0], 100) * 10**3
+    )
+
+
+if __name__ == '__main__':
+    test_basic()
+    test_embedded()