Validate multiple contexts on `valid?` and `invalid?` at once.

Example:

```ruby
class Person
  include ActiveModel::Validations

  attr_reader :name, :title
  validates_presence_of :name, on: :create
  validates_presence_of :title, on: :update
end

person = Person.new
person.valid?([:create, :update])    # => true
person.errors.messages               # => {:name=>["can't be blank"], :title=>["can't be blank"]}
```

1 files changed, 5 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/validations.rb b/activerecord/lib/active_record/validations.rb
index 34d96b19fe..108fe548c8 100644
--- a/activerecord/lib/active_record/validations.rb
+++ b/activerecord/lib/active_record/validations.rb
@@ -54,7 +54,7 @@ module ActiveRecord
     # Validations with no <tt>:on</tt> option will run no matter the context. Validations with
     # some <tt>:on</tt> option will only run in the specified context.
     def valid?(context = nil)
-      context ||= (new_record? ? :create : :update)
+      context ||= default_validation_context
       output = super(context)
       errors.empty? && output
     end
@@ -63,6 +63,10 @@ module ActiveRecord
 
   protected
 
+    def default_validation_context
+      [new_record? ? :create : :update]
+    end
+
     def raise_validation_error
       raise(RecordInvalid.new(self))
     end