RSpec tests in custom engines are not being run

[kristinalim]

The rspec command which we use does not run tests of custom engines in engines/web.

Description

#2521 (following this discussion) introduced custom engines representing domains. That added the new "web" engine in engines/web. However, the custom engine is not covered by the rspec command which we run and is used by the official CI accounts.

Tests in custom engines should be run.

Expected Behavior

1. GETTING_STARTED should document testing the custom engines.
2. The Travis CI configuration file should run RSpec tests in the custom engines.

Actual Behavior

These are not the case.

Steps to Reproduce

Only for developers:

1. Introduce a failing test in engines/web/spec/ and push to Semaphore and Travis.
2. There are no failing tests in Semaphore and Travis.

Context

I added a new custom engine "Order Management" for #2616 and noticed that the engine tests were not covered by our CI configurations.

Severity

bug-s5: we can live with it, only a few users impacted