use tempfile module

mrbgems/mruby-bin-mruby/bintest/mruby.rb

+require 'tempfile'
+
 assert('regression for #1564') do
   o = `bin/mruby -e '<<' 2>&1`
   assert_equal o, "-e:1:2: syntax error, unexpected tLSHFT\n"
@@ -6,8 +8,9 @@ assert('regression for #1564') do
 end
 
 assert('regression for #1572') do
-  system "echo 'p \"ok\"' > /tmp/1572.rb"
-  system "bin/mrbc -g -o /tmp/1572.mrb /tmp/1572.rb"
-  o = `bin/mruby -b /tmp/1572.mrb`.strip
+  script, bin = Tempfile.new('test.rb'), Tempfile.new('test.mrb')
+  system "echo 'p \"ok\"' > #{script.path}"
+  system "bin/mrbc -g -o #{bin.path} #{script.path}"
+  o = `bin/mruby -b #{bin.path}`.strip
   assert_equal o, '"ok"'
 end