Enable parallel testing

[NullVoxPopuli]

Using context keyed off of this,

const ContextMap = new WeakMap();

function getContext<T>(test: obj): T {
  let context = ContextMap.get(test);
  if (!test) {
    context = {};
    ContextMap.set(test, context);
  }
  return context as T;
}

each tests' this gets its own context, which means all unit, rendering, and application tests can run in parallel.

[NullVoxPopuli]

if we require a class for managing the this, then we can do this is a non-breaking opt-in change.

Existing testing keeps using module/test/etc, but those using the class could get parallel testing along side their existing module/test/etc