Add test_on and test_onload convenience functions.

[jgraham]

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[hallvors]

Isn't the order of arguments a little..odd? It's closely related to addEventListener which has event type, function - and here we suddenly reverse it to function, object, type ..?

test_on(window, 'DOMContentLoaded', function(){ ... }, 'Test ...')

I would find easier to remember by association.

[jgraham]

So the reasoning is that it matches all the other test* functions that always take the test function as their first argument (did that sentence make sense). I agree it feels a bit odd in this case though.