Split test module into smaller modules

[roy-mor]

Currently all unit tests reside in one file and it is too large. The test module should be split into smaller, separate files, based on area/feature being tested (gql-generator tests, router tests, various capabilities etc).

When invoking npm test all tests from all these files should be executed.

Test components should be shared across files as much as possible (mocha, chai, runMiddleware, mocks etc).

[roy-mor]

Closed thanks to contribution from @SergSisense. Thanks!