several unit test sets use an object to store the tests + expected. ...

JavaScript does not warn nor fail when in the same definition an attribute is indexed by number and by string: the last one wins. This essentially SILENTLY REMOVES test cases from the set.

Here is a dump of a minimal line of JS code exhibiting the problem; the second line is the output in Chrome:

    x = { 1: 7, '1': 9 }

    Object {1: 9}