[META] Rewrite test modules in system to provide better unit testing.

Problem/Motivation

We got 50 test modules inside system module to test various core operation. However this modules written in D7 way and converting them as it is to D8 might not be very efficient.

Proposed resolution

Rewrite the modules so that it can be well unit-tested and stand as a reference modules for contrib module developers to port their modules into D8.

Remaining tasks

1. Need discussion on rewrite.

Modules

1. ajax_forms_test
2. ajax_test
3. batch_test
4. bundle_test
5. cache_test
6. common_test
7. common_test_cron_helper
8. condition_test
9. config_upgrade
10. database_test
11. design_test
12. drupal_system_listing_compatible_test
13. drupal_system_listing_incompatible_test
14. entity_cache_test
15. entity_cache_test_dependency
16. entity_crud_hook_test
17. entity_test
18. error_test
19. form_test
20. image_test
21. menu_test
22. module_autoload_test
23. module_test
24. paramconverter_test
25. path_test
26. plugin_test
27. requirements1_test
28. requirements2_test
29. router_test
30. serialization_test
31. session_test
32. system_dependencies_test
33. system_incompatible_core_version_dependencies_test
34. system_incompatible_core_version_test
35. system_incompatible_module_version_dependencies_test
36. system_incompatible_module_version_test
37. system_mail_failure_test
38. system_module_test
39. system_test
40. taxonomy_test
41. test_page_test
42. theme_page_test
43. theme_test
44. transliterate_test
45. twig_theme_test
46. update_script_test
47. update_test_1
48. update_test_2
49. update_test_3
50. url_alter_test

User interface changes

Hopefully not.

API changes

N/A

Original report by @dawehner

IRC chat:

[14:03] <dawehner> vijaycs85: hi
[14:03] <dawehner> vijaycs85: even more important: having proper unit tests would make things way faster to test
[14:04] <dawehner> vijaycs85: and the amount of custom test code would be reduced etc.
[14:04] <vijaycs85> dawehner: agreed... however we might need to start it as a meta :)
[14:05] <dawehner> vijaycs85: good point
[14:05] <vijaycs85> dawehner: oh god.. we got 48 MODULES!!!
[14:05] <dawehner> vijaycs85: you know, at the same time a lot of the custom functions should be maybe ported to a proper more d8 like api
[14:06] <dawehner> vijaycs85: so it's maybe hard to crowd-source these tasks?
[14:06] <dawehner> in the sense of: it's hard to describe generically what to do
[14:10] <vijaycs85> dawehner: I guess,  this modules are going to be first of its kind and it good as in  we will have something to refer in core and bad, it takes time as it is first
[14:11] <vijaycs85> dawehner: however keeping old module and trying to convert every piece of it also sounds not fun - may lead to bad example of D8 module
[14:11] <dawehner> vijaycs85: right
[14:12] <vijaycs85> dawehner: may be we can start a meta and try to see how long we can go? :)
[14:13] <dawehner> yeah,  a meta would certainly help
[14:13] <dawehner> vijaycs85: i guess it's also important to set these issues to postponed or something like that, so people don't waste their time
[14:14] <vijaycs85> dawehner: agreed.. I will update them...
[14:18] <dawehner> vijaycs85++
[14:30] <vijaycs85> dawehner: totally 83 defects (out of 148) are test modules :)
[14:30] == Artusamak has changed nick to Artusamak_afk
[14:31] <dawehner> vijaycs85: well test modules are for itself not bad, as they even provide some example code
[14:31] <dawehner> but yeah on the longrun they for sure have to be more like proper d8 code
[14:32] <vijaycs85> dawehner: okay