$ cat mu_1
require 'miniunit'

include Test::Unit::Assertions

def foo(a)
  assert_instance_of String, a, "testing argument 'a'"
  puts a
end

begin
  foo(1)
rescue => e
  puts "\n#{e.inspect}"
end

begin
  foo(nil)
rescue => e
  puts "\n#{e.inspect}"
end

exit



$ mu_1
mu_1:1:in `require': no such file to load --
   miniunit (LoadError)  from mu_1:1