Update tests for TW Experimental

Tests for TW experimental will now run on Travis CI.

There's also a fix for a bug in `_load_task` that I discovered while running the tests.

There are still issues with Python 3 but the tests should run OK in Python 2.7 with 4 failures. There are TODOs where I could use some help (for example, skipping some tests that don't apply to TW experimental).