[TEST] add visualization non regression tests for missing supported BPMN elements

[tbouffard]

526 introduced the way to do that new kind of tests but some BPMN elements supported by the library are not covered.

BPMN elements to cover

• [x] events (#543): all types including start events in event subprocess. See below for an example
• [x] #607 content of subprocess, including inner subprocesses, lanes. See existing examples in https://github.com/process-analytics/bpmn-visualization-examples/tree/4086f6f9eda8e1067061b59baacd3a2135318dd5/bpmn-files
• [x] #627 and #624 text annotation - with labels
• [x] #624 associations
• flows
  • [x] #626 sequence flow: add complex paths, see #295 for instance
  • [x] #626 sequence flow types (default, conditional)
  • [x] #625 message flow: add complex paths and labels
• [x] #584 documentation update: contribution guide
  • there is no guide line about this new type of tests
  • when and how to add tests
  • how and when to configure diff image threshold (some explanations are present in the code, but is this enough?)
  • avoid labels in tests, avoid markers and icons on BPMN elements when not related to the test (more subject to changes, so tests will break whereas they are not testing this feature)
  • load method: explain when choosing a dedicated method and how to configure
  • default: pass content via url
  • larger file: via fetch

BPMN events test proposal

Covered by #543

Note: because of an issue with some bpmn file (see below), the file cannot be used as it is. If no solution is found, it should be splitted by types: start event, intermediate, events in event subprocess, ...

bpmn file: events.bpmn.zip

Current issue with quite large BPMN content

Covered by #543

This has been detected while creating #540 Because we currently pass the bpmn content via an url parameter, we often get an http 400 error from the dev server when the BPMN diagram is too large.

• Length 5153: OK
• Length 5421: KO

[tbouffard]

All tests noticed here have been implemented. So closing this issue