[19.0][FIX] account_invoice_report_grouped_by_picking: convert grouped qty to invoice line UoM

[rwagemans]

Bug

lines_grouped_by_picking sums and subtracts the stock move quantity returned by _get_signed_quantity_done (expressed in the move's UoM, i.e. the product's stock UoM) against line.quantity / remaining_qty (expressed in the invoice line UoM), without converting between the two:

remaining_qty = line.quantity            # invoice line UoM (e.g. 2 packs)
for move in line.move_line_ids:
    qty = self._get_signed_quantity_done(line, move, sign)  # move.quantity in stock UoM (e.g. 12 units)
    picking_dict[key] += qty             # printed in stock UoM
    remaining_qty -= qty                 # 2 - 12 = -10
...
if remaining_qty:                        # -10 is truthy
    lines_dict[line] = remaining_qty     # phantom remainder line

When the invoice line UoM differs from the product's stock UoM (e.g. selling in packs/pallets while stock is kept in units), two things go wrong:

1. The per-picking quantity is printed in the stock UoM instead of the invoice line UoM.
2. A bogus remainder line with a negative quantity is produced, because a stock-UoM quantity is subtracted from an invoice-line-UoM quantity.

It goes unnoticed in the common case where both UoMs are equal.

Fix

_get_signed_quantity_done now converts the move quantity to the invoice line UoM before it is summed/subtracted. A regression test (test_account_invoice_group_picking_uom_conversion) covers a product sold per pack of 6 while delivered in units: exactly one group, expressed in packs, with no phantom remainder line.

Test

account_invoice_report_grouped_by_picking test suite: 6/6 green.

[pedrobaeza]

Please don't change manually the module version. It's done on merge.

[BhaveshHeliconia]

LGTM!

[pedrobaeza]

As no conflict has arisen with the module version change, let's merge with nobump:

/ocabot merge nobump

[OCA-git-bot]

Hey, thanks for contributing! Proceeding to merge this for you.
Prepared branch 19.0-ocabot-merge-pr-424-by-pedrobaeza-bump-nobump, awaiting test results.

[OCA-git-bot]

Congratulations, your PR was merged at 6699a21. Thanks a lot for contributing to OCA. ❤️