src/third_party/mozjs-45/js/src/jit-test/tests/basic/testStringBufferMallocAccounting.js

// first build a big honkin' string
str = "a";
for (var i = 0; i < 20; ++i)
    str = str + str;
str.indexOf('a');

var f;
f = makeFinalizeObserver();
assertEq(finalizeCount(), 0);

// Create another observer to make sure that we overwrite all conservative
// roots for the previous one and can observer the GC.
f = makeFinalizeObserver();

// if the assert fails, add more iterations
for (var i = 0; i < 80; ++i)
    str.replace(/(a)/, '$1');
//assertEq(finalizeCount(), 1);