[x] For test samples, allow the run button to mean "run my tests".
[x] Allow tests to be hidden and the implementation editable to teach test-driven problem solving.
[x] Allow the tests to be visible and the implementation hidden to teach test-driven ways of exploring existing behaviors.
[x] We would want a way to display test results that's a little more interesting than the current console output.
Reference: https://github.com/dotnet/try/issues/94