As part of the Hack Days this year my colleague Falko migrated an existing tool we (Camunda Consulting) used with success in a lot of projects to bpmn.io: The Process Test Coverage Report Generator. It just hooks into an automated test (typically JUnit) and creates an HTML report showing the coverage:
For every Test Case
For the whole Test Suite
See this example for one test case - obviously the Happy Path of the process model:
The report can easily be watched locally within your IDE or hooked into your Jenkins Build. See GitHub Readme for details.
By the way - our Best Practice is to go for “Flow Node Coverage” - so your Test Suite should “visit” each BPMN Flow Node (Events, Activities, Gateways, …) at least once.