assert_rjs :call on something more complex than 'foo' 'bar'

Raileanos:

Suppose I want to insert JS into an RJS page object (which I call
'rjs' to distinguish it from all the many other 'page' objects in the
universe). The production code looks like this:

    rjs << 'Element.setStyle("myDiv"), { backgroundColor: "blue" };'

So what's the test-side supposed to look like? This??

    assert_rjs :call, 'Element.setStyle', 'myDiv', '{ backgroundColor: "blue" }'

That ain't working. The {} jigger is JSON, right? How do we match the {}?