For some reason unknown to me, the following commit added logic to make
sure that negative fees never make the order total negative: 804feb9333
Probably by accident, commit 4326e39250 changed this logic when `$fees_total += $item->get_total()` was replaced by `$fees_total += $fee_total`:
4326e39250 (diff-9b4164165828b26c4b7aec01c7b17884R1594)
This commit adds a failing test that ensures that the old behavior is
tested. This test needs to be fixed before we merge the changes proposed
in PR #25504.
* Add functionality to wp-admin order to check for coupon usage based on email addresses, similar to how WC_Cart handles this seperately, included unit tests.
* Only do the coupon by email usage check if order is from a guest. Fix issue with unit test.
This commit adds the exception message thrown when WC_Order::set_billing_email() is called with an invalid message to a test to fix it.
I couldn't find what change in WC codebase broke the test and I'm not sure why it is failing only when running using PHP 5.6:
https://travis-ci.org/woocommerce/woocommerce/jobs/315750242#L600