cubicweb #7817147 Remove assert in CubicWebTC.config (about direct usage of the class) [validation pending]

The point is to be able to use other test runners (e.g. nose2, nosetests, py.test) with CubicWebTC.

The (first) stumbling block is the presence of assertions in CubicWebTC preventing direct usage of the class (without subclassing) (see first comment in #2502531). These assertions could just be removed (in my opinion).

Another solution is to avoid importing CubicWebTC directly but rather import the testlib (see #6007665 for instance), but this is cumbersome and would require a lot of work for downstream projects.

prioritynormal
typeenhancement
done in3.22.0
load1.000
load left0.000
closed by#b71511460a4f [devtools/testlib] Remove assertions about direct usage of CubicWebTC/AutomaticWebTest
patch[devtools/testlib] Remove assertions about direct usage of CubicWebTC/AutomaticWebTest [applied]