added test.py

test.py

@@ -0,0 +1,11 @@
+from calibrestekje import Book, Publisher, init_session
+
+session = init_session("sqlite:///metadata.db")
+
+publisher = (session.query(Publisher)
+                    .filter(Publisher.name == "MIT Press").one())
+
+books = (session.query(Book)
+                .filter(Book.publishers.contains(publisher)))
+
+print(f"Books published by MIT Press: {books.count()}")