[Enhancement] More info in failing tests.

[whizzzkid]

While debugging #129 the test suite did not give enough info on what calls were failing, the final fixes were added in:

• 3b1cccd
• dc52e2f

This could have been simpler if the test runner reported the call order in the failure scenario.

### Tasks
- [ ] Add call index count on what actually failed. `call #3 did not have proper args:`
- [ ] optionally Add stack trace on other calls in progress.