Fixes#2876 with @paulmelnikow's suggestion
Moved imports of `ServiceTester` and `createServiceTester` to a separate file so that dev dependencies are not imported by service classes.
Continue to implement #2698:
- Add `core/base-service/index.js` (but hold off on moving the things it imports)
- Add shortcuts in `services/index.js` for Base*Service, errors, and deprecatedService. This file will be streamlined later to avoid cluttering it with rarely used bits.
- Apply consistent ordering of imports and use of `module.exports` in testers.
- Remove some renaming of imports.
- Remove obsolete tests here and there.
The GitHub service family is the largest, and as yet untouched by our service rewrite. I thought I would start the process by tackling one service.
This pull request has a few things going on:
1. Rename pull-request-status to pull-request-check-state. We have another badge called pull request status. It seems like the checks are called one thing in the UI and another thing in the API, which is unfortunate. If other folks have strong feelings about the name, I’ll defer.
2. Move its tests and tighten up the syntax.
3. Move its badge examples including the doc string.
4. Add a new helper `errorMessagesFor` to use in the new services in place of `githubCheckErrorResponse`. It seems like we didn’t really use the `errorMessages` parameter to `githubCheckErrorResponse`, so I pared this down. I’m not sure if this is the function we’ll ultimately want, but it seems like a good place to start.
5. Pull fetch code I _know_ we use in other places into `github-common-fetch`. As in the PR I just opened for azure-devops, this takes a functional approach to the shared code, which is more direct, nimble, and easy to reason about than inheritance.
6. Create `GithubAuthService` which functions identically to BaseJsonService, except for one thing, which is that it uses the token pool. I accomplished this by adding a `_requestFetcher` property to BaseService, which is initialized to `sendAndCacheRequest` in the constructor, and can be overridden in subclasses. Since we weren’t using `_sendAndCacheRequest` directly except in BaseService and tests, I removed that property. I like this approach to patching in the GitHub auth because it’s very simple and creates no new API exposure. However, the way we’re doing the dependency injection feels a bit odd. Maybe the eventual refactor of request-handler would be a godo time to revisit this.
The GitHub requests go through many, many layers of indirection at this point. Later on it would be good to shave some of these off, perhaps once the legacy GitHub services have been converted, or when all the services are done and we can take another look at the base service hierarchy. The work in #2021 and #1205 is also related.
