module Rails::Generators::Testing::Assertions

def assert_no_file(relative)

assert_no_file "config/random.rb"

path relative to the configured destination:
Asserts a given file does not exist. You need to supply an absolute path or a 
def assert_no_file(relative)
  absolute = File.expand_path(relative, destination_root)
  assert !File.exist?(absolute), "Expected file #{relative.inspect} to not exist, but does"
end