Check and update test coverage of Xero Invoices report

[lin-d-hop]

What we should change and why (this is tech debt)

To reduce the task of testers we wish to check the test coverage of reports. Xero Invoices report: https://github.com/openfoodfoundation/openfoodnetwork/blob/master/spec/lib/open_food_network/xero_invoices_report_spec.rb https://github.com/openfoodfoundation/openfoodnetwork/blob/master/spec/controllers/spree/admin/reports_controller_spec.rb.

Tests should cover all filter options in the UI.

Context

Reducing manual testing task.

Impact and timeline

Agreed in Brussels (FOSDEM2020) to continually one issue to increase test coverage exists in the delivery pipe. Priority will be reports and code areas that frequently lead to S1s and S2s.

[RachL]

@filipefurtad0 I'm trying to reduce the number of issues in our repository (new contributors interpretation of he number of issue is that we don't update our repo very often). Would it make sense to keep as open issue, just a big epic listing all reports, and we open individual issues only when starting to work on it?

[lin-d-hop]

Closing, reports have much better test coverage now