Extract `appendView`, `destroyView` for testing

Defining `appendView` and `destroyView` in multiple tests is verbose, 
repetitious, and copy-paste-error prone.
@rwjblue how do you feel about renaming the exported functions?

Their value comes from the fact that they're wrapped in a `run` block.

`appendView` -> `runAppend`?
`destroyView` -> `runDestroy`?