though
    assert_array_equal(a,b)
is ok, the regexp will fail for any space inside the parentheses
So any of these will fail:
    assert_array_equal(a, b)
    assert_array_equal(a,b )
    assert_array_equal( a, b )
I guess you need a couple of "\s*" in the regexp.
btw, it would be great if one could enter anything, not just "words" in there (ie arrays, function calls
etc).
Thank you.