Allow login_as helper to accept a User object

spec/support/login_helpers.rb

 module LoginHelpers
-  # Internal: Create and log in as a user of the specified role
+  # Internal: Log in as a specific user or a new user of a specific role
   #
-  # role - User role (e.g., :admin, :user)
-  def login_as(role)
-    @user = create(role)
+  # user_or_role - User object, or a role to create (e.g., :admin, :user)
+  #
+  # Examples:
+  #
+  #   # Create a user automatically
+  #   login_as(:user)
+  #
+  #   # Create an admin automatically
+  #   login_as(:admin)
+  #
+  #   # Provide an existing User record
+  #   user = create(:user)
+  #   login_as(user)
+  def login_as(user_or_role)
+    if user_or_role.kind_of?(User)
+      @user = user_or_role
+    else
+      @user = create(user_or_role)
+    end
 
     login_with(@user)
   end