module ActiveModel::Validations

def validate!(context = nil)

some :on option will only run in the specified context.
Validations with no :on option will run no matter the context. Validations with

no errors are found, raises +ValidationError+ otherwise.
Runs all the validations within the specified context. Returns +true+ if 
def validate!(context = nil)
  valid?(context) || raise_validation_error
end