The breaking change page wasn’t properly accounting for the fact that
letter recipients span multiple columns – it was assuming they’d only
take up one column like they do for email and SMS.
This commit fixes:
- the number of column headers (A, B, C, …) to be correct
- the count of columns (you will need X columns in your file) to be
correct
It then parameterises the test to look at a case where a recipient is
in one column (email) and multiple columns (letter).