function test() {

// [[Set]] -> [[DefineOwnProperty]]
var def = [];
var p = new Proxy({foo:1, bar:2}, { defineProperty: function(o, v, desc) { def.push(v); Object.defineProperty(o, v, desc); return true; }});
p.foo = 2; p.bar = 4;
return def + '' === "foo,bar";
      
}

if (!test())
    throw new Error("Test failed");