* chore: Add Windows to Travis
This commit runs the unit tests on Windows.
There are two tests failing on Windows that we skip.
I spoke to Mathias B and we agreed to
defer debugging this for now in favour of getting tests running on
Windows. But we didn't want to ignore it forever, hence giving the test
a date at which it will start to fail.
Rather than maintain our own test runner we should instead lean on the community and use Mocha which is very popular and also our test runner of choice in DevTools too.
Note that this commit doesn't remove the TestRunner source as it's still used for other unit tests, but they will be updated in a future PR and then we can remove the TestRunner.
The main bulk of this PR is updating the tests as the old TestRunner passed in contextual data via the `it` function callback whereas Mocha does not, so we introduce some helpers for the tests to make it easier.
