Add benchmark script

test/bench_execjs.rb

@@ -0,0 +1,20 @@
+require 'benchmark'
+require 'execjs'
+
+TIMES = 10
+SOURCE = File.read(File.expand_path("../fixtures/coffee-script.js", __FILE__)).freeze
+
+Benchmark.bmbm do |x|
+  ExecJS::Runtimes.runtimes.each do |runtime|
+    next if !runtime.available? || runtime.deprecated?
+
+    x.report(runtime.name) do
+      ExecJS.runtime = runtime
+      context = ExecJS.compile(SOURCE)
+
+      TIMES.times do
+        context.call("CoffeeScript.eval", "((x) -> x * x)(8)")
+      end
+    end
+  end
+end