Indicates that the demo or test should be run as the specified user, with the specified roles.
Note: this fixture does not in itself do anything (its {@link #install()} isa no-op). However, if present in the fixture list then is "noticed" by the framework, and is used to automatically logon when the framework is booted (providing running in prototype or exploration, not in production).
To change the user during the installation of fixtures, either use {@link SwitchUserFixture}.
@see SwitchUserFixture