Create test specs for User model.
Create test specs for User model.

+ Create spec to verify that a new user is added to the 'users' table correctly.
+ Create spec to verify that a user cannot be added without a username.
+ Create spec to verify that a user cannot be added if the username is not unique.
+ Create spec to verify that a user cannot be added without an email.
+ Create spec to verify that a user cannot be added if the email is not unique.
+ Create spec to verify that a user cannot be added without a password.
+ Create spec to verify that a user cannot be added if the password is not unique.
+ Create spec to verify that the user can be updated.
+ Create spec to verify that the user can be deleted.

andela-ioraelosi/hackshub-file-user-service