diff --git a/foo.rb b/foo.rb
index 448258a..08e4933 100644
--- a/foo.rb
+++ b/foo.rb
@@ -1,10 +1,11 @@
-s = 0
-10.times do |x|
-  s += x
+def run(num)
+  if num == 45
+    p :ok
+  else
+    p :ng
+  end
 end
 
-if s == 45
-  p :ok
-else
-  p :ng
+def fuzz(bytes)
+  run(bytes[0])
 end
diff --git a/run.rb b/run.rb
index 08feb5b..74890b5 100644
--- a/run.rb
+++ b/run.rb
@@ -2,9 +2,13 @@
 
 require 'coverage'
 
-Coverage.start(:all)
-# Coverage.start(branches: true)
-# Coverage.start(methods: true)
-# Coverage.start(lines: true)
-load('foo.rb', true)
-p Coverage.result
+fork do
+  Coverage.start(:all)
+  load('foo.rb')
+
+  fuzz(Random.new.bytes(10))
+
+  p Coverage.result
+end
+
+Process.wait