This commit simply adds a small test for the import multi-mapping feature that
allows the end-user to map multiple columns of his import file to the same
field.
The values in the files are merged together, meaning concatenated for Char/Text
fields and accumulated for Many2many fields.
This commit is done as a preliminary step before fixing an issue related
to this feature in v15.
Task-2687407
closesodoo/odoo#79913
X-original-commit: ac832586e68e0873d69c0b10a3f8cc8b08ea506e
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>