failing test for joining digits together string-like base 10
dammit, dash maps to underscore
misplaced bracket!
make the tests pass
basic tests for finding sum combinations from groups of objects
some possible failure cases
woops
make the tests pass
we only need the count - this uses less memory
a test for the problem's answer
all this is unnecessary now
some tests to describe the filtering for checking if things are products
make them pass
some tests for this somewhat strangely signatured function
make that strange function work