How to enable Ruby warnings in Rails?

I did this in test.rb:

def some_method
  p "First definition"
end

def some_method
  p "Second definition"
end

some_method

When I call ruby test.rb, it prints Second definition (expected)

When I call ruby -w test.rb, it prints Second definition (expected) and prints a warning test.rb:5: warning: method redefined; discarding old some_method

Is there a way to enable those warnings in Rails? (and print the warning to the console/log file)

Why I would like to enable warnings: For example if I inadvertently re-define a method in a controller, then I would be aware of the problem by looking at the warning printed to the console/log file. See here for an example.