Add line item level allowance charge

[phillipp]

The standard allows for AllowanceCharge on the line item level. This is now added and must be an array, because there can be multiple AllowanceCharges (think multiple discounts).

The base_amount is optional in the standard, so we don't require it anymore.

[phillipp]

@corny Many of the bugs I fixed were simple adjustments to the XML that weren't detected because only a single top-level document is run through the validator. The fact that both specs and the validator exist can lead to either not using the validator or overlooking it entirely.

Additionally, it's a bit tedious that XML files always have to be edited for testing. Some of the XML files in spec/fixtures/scraps don't even match the spec, making it impossible to verify overall correctness properly.

My suggestion would be to restructure the testing setup so that the validator runs in daemon mode, and all tests build a complete document. This document would then be tested against the web interface. Request/response pairs would be recorded using VCR, making tests fast and eliminating the need for a local server when only changing code.

This would ensure that all generated XML is truly valid. What do you think?

[corny]

I prefer to start the validator in a service container that must be running during the specs.

[phillipp]

@corny was just asking what yourt preference was, this pull is not affected by this and can be merged ;-)