Testing Bank Statement Parsers With Opening-to-Closing Balance Tie-Outs

A DEV Community author argues that the most reliable way to test a bank statement parser is a tie-out, where the printed opening balance plus extracted transactions must equal the printed closing balance exactly. The method is presented as more useful than vendor accuracy percentages, which are often unexplained and not reproducible. The article advises using exact decimal arithmetic instead of floats, tying out each account separately, and normalising debits and credits into a single signed amount column. It includes a runnable Python example with a diagnostic step that uses the size of a balance gap to suggest likely errors such as duplicated, missing, or swapped-sign rows. The author discloses that they work on one of the twelve converters evaluated, which ranked itself first.