The workflow for “pay a bill in Doccle”, drawn as a metro map instead of code. Follow one Telenet invoice down the happy flow, then down every edge case and error the developers handled, and see which tracks can be built next.
How to read it. Green is the happy flow. Orange side tracks are unusual cases that are handled and rejoin the main line. Red tracks stop: something went wrong. Grey dotted tracks are ideas, not built yet. Point at any stop for what it does, the data it touches and the tests that cover it.
A mock-up to show the idea: Sarah, the invoice, the amounts, the volumes and the test counts are made up, and Telenet's and Doccle's marks are simplified.