Update user resolver tests to be more robust and have higher confidence

Previously, the apollo-server-testing was used for the tests. This had key limitations, such as non-access to context without a low-confidence workaround (see apollographql/apollo-server#2277 fof more info). This limitation also made creating some tests, such as ?should return current user if logged in" impossible. To resolve, migrate to https://github.com/zapier/apollo-server-integration-testing and create the tests that were previously impossible.

* Update queries-mutations constant with queries/mutations for new tests
* refactor the user.test file to remove old approach
* add missing test coverage