add unittest for core_collapse
related to #41
#41
core-ajax-dart unittest (fails with `<debug target crashed>`
Merge branch 'master' of github.com:dart-lang/core-elements
rename test core_ajax to core_ajax_dart
update unit test according to the comments in #43
Merge pull request #47 from zoechi/master

add unittest for core-ajax-dart and core-collapse