More gracefully handle load errors.

CHANGELOG.md

 ### 0.12.0-beta.6
 
 * Add the ability to run multiple test suites concurrently. By default a number
   of concurrent test suites will be run equal to half the machine's processors;
   this can be controlled with the `--concurrency` flag.
 
+* Expose load errors as test failures rather than having them kill the entire
+  process.
+
 * Add support for running tests on Firefox.
 
 ### 0.12.0-beta.5
 
 * Add a `--pub-serve` flag that runs tests against a `pub serve` instance.
   **This feature is only supported on Dart `1.9.2` and higher.**
 
 * When the test runner is killed prematurely, it will clean up its temporary
   directories and give the current test a chance to run its `tearDown` logic.
 
@@ skipping 166 matching lines @@
 * **NEW!** `expectAsyncUntil` replaces the now deprecated `expectAsyncUntil0`,
     `expectAsyncUntil1` and `expectAsyncUntil2`
 * `TestCase`:
     * Removed properties: `setUp`, `tearDown`, `testFunction`
     * `enabled` is now get-only
     * Removed methods: `pass`, `fail`, `error`
 * `interactive_html_config.dart` has been removed.
 * `runTests`, `tearDown`, `setUp`, `test`, `group`, `solo_test`, and
   `solo_group` now throw a `StateError` if called while tests are running.
 * `rerunTests` has been removed.