Test of spec language from 15.4.4.4,
5.b.iii.3.b states 'Call the [[DefineOwnProeprty]] internal method of A'
which means that the result of Array.prototype.concat
should return `true` from `hasOwnProperty` for every property
created by `concat`, up to `length`

Set length to 3.
a[0] is set to 0 on a
a[1] is unset
a[2] is set to 2 via a prototype of a

add assertions for values of b[0], b[1], b[2]
add assertions for b.hasOwnProperty('2')

Check with Array.prototype and Object.prototype, separate tests

fix typo in assertion message

test was correct, but assertion message was incorrect