A cheap class method call tracing instrumentation (without using doubles)

class_method_instrumentation.rb

# Example of use to detect a class method call throughout a whole test suite
# This could also be achieved with a RSpec double.
class Dir
  old_method = method(:[])
  
  define_singleton_method(:[]) do |*args|
    # Use failure in a test-suite where you'd need to detect use
    fail "FIXME - Dir[] called with args #{args.inspect}"
    # Or call through using this, if you only need to trace
    # old_method.call(*args)
  end
end