The idea of splitting integration from unittests is good in theory
but leads to a lot of mental overhead. Besides whenever a tests
interacts with a database it isn't a unittest anyway.

Better to use filenames which are commonly used in the python word then
custom ones.

Fixes stockrecord availability validation message in the case when stock is lower than allocation. Previously the message that appeared contained negative numbers. For example: "a maximum of -1 can be bought". Now it will display: "no stock available"

Also make the availability warnings start with a lowercase char so they
can be embedded in other sentences easily.

Rather than a StockRecord instance.  This makes it much simpler.

This are to replace the partner wrappers.