Fix test typo and expand test cases for `Rememberable#rememberable_value`.

Closes #4157

test/models/rememberable_test.rb

@@ -99,15 +99,28 @@ class RememberableTest < ActiveSupport::TestCase
     assert_nil User.serialize_from_cookie(user.to_key, "123", Time.now.utc)
   end
 
+  test 'raises a RuntimeError if the user does not implements a rememberable value' do
+    user = User.new
+    assert_raise(RuntimeError) { user.rememberable_value }
+
+    user_with_remember_token = User.new
+    def user_with_remember_token.remember_token; '123-token'; end
+    assert_equal '123-token', user_with_remember_token.rememberable_value
+
+    user_with_salt = User.new
+    def user_with_salt.authenticatable_salt; '123-salt'; end
+    assert_equal '123-salt', user_with_salt.rememberable_value
+  end
+
   test 'raises a RuntimeError if authenticatable_salt is nil or empty' do
     user = User.new
-    def user.authenticable_salt; nil; end
+    def user.authenticatable_salt; nil; end
     assert_raise RuntimeError do
       user.rememberable_value
     end
 
     user = User.new
-    def user.authenticable_salt; ""; end
+    def user.authenticatable_salt; ""; end
     assert_raise RuntimeError do
       user.rememberable_value
     end