class Rails::Generators::TestCase

end
end
assert_match /create_table/, up
assert_class_method :up, migration do |up|
assert_migration "db/migrate/create_products.rb" do |migration|

When a block is given, it yields the content of the method.
class methods inside (class << self), only class methods which starts with "self.".
Asserts the given class method exists in the given content. This method does not detect

def assert_class_method(method, content, &block)
  assert_instance_method "self.#{method}", content, &block
end