Your task is to implement a registration service and write unit tests for it.

Registration service has one method register(User user), that accepts some user (the User.class has already been given to you). This method should register a user (by adding it to Storage) only if the user meets the following criteria:

• there is no user with such login in the Storage yet
• the user is at least 18 years old
• user password is at least 6 characters

In case of invalid data you should throw RuntimeException.

Storage and class StorageDaoImpl for working with the Storage has already been implemented. It has two methods:

• User add (User user) - which adds a user to the storage
• User get (String login) - which gets the user from the storage by login or returns null if there is no such user.

Your task is to write as many tests as possible to cover all possible options.

There are a lot of ways to name your test methods. The main point is that they should have informative names and be consistent along with other developers in your team. For this task use such convention: <methodUnderTest>_<state>_<expectedBehavior>; For example, if we are testing the method register with a null
user's age the test method name should be register_nullAge_notOk. notOk is because the test expects the register method to throw an exception.