[#1117] Typo
[#1117] Make various improvements to test_update.py

- Add some notes to the top of test_update.py about what I'm trying to do with
  it, these will end up in the testing guidelines
- Make the static test data read-only
- Rename some of the test methods so that they're all test_user_update_*
- Add test_user_update_activity() test
- Other small tweaks