question about spy on a function

[fool2fish]

in api doc, it is said a spy could be created by this way:

var spy = sinon.spy(myFunc);
Spies on the provided function

my code:

function a(){}
function b(){}
function fn(args){
    args ? a(args) : b(args)
}
var spy = sinon.spy(a)
it('excute function a if args is true', function(){
    fn(1)
    expect(spy.calledOnce).to.be.ok() // failed
    fn(true)
    expect(spy.calledTwice).to.be.ok() // failed too
})

why?

[mantoni]

sinon.spy returns a new function which wraps the given function. You would have to call the returned function so that Sinon can cound calls for you.

[fool2fish]

3ku

but can some examples could be given to show that sinon.spy() and sinon.spy(fn) are useful in practice？

[cjohansen]

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