Problem

GitHub.Sync.installation_event/1 is currently completely untested. Since we want to unit test its individual elements to, it should suffice to test each possible outcome of the transaction performed by the tests, as defined by GitHub.Sync.installation_event_outcome()

Subtasks

• write tests for {:ok, GithubAppInstallation.t()} outcome
• write tests for {:error, :validation_error_on_syncing_installation, Changeset.t()} outcome
• write tests for {:error, :multiple_unprocessed_installations_found} outcome
• write tests for {:error, :github_api_error_on_syncing_repos, struct} outcome
• write tests for {:error, :validation_error_on_deleting_removed_repos, {list, list}} outcome
• write tests for {:error, :validation_error_on_syncing_existing_repos, {list, list}} outcome
• write tests for {:error, :validation_error_on_marking_installation_processed, Changeset.t()} outcome
• write tests for {:error, :unexpected_transaction_outcome, any} outcome