Improved dependency resolver and tests

[epdenouden]

Summary

Changes to test execution order can result in unexpected defects and create uncertainty, which is the exact opposite of what we want. The dependency resolver is improved to be more hands-off and leave more tests in original order.

Why: backwards compatibility

During development of the test execution reordering feature #3092 backwards compatibility was discussed. Automatic dependency resolution will be optional in 7.x and default for 8.x.

How: improved dependency manager

The current resolver has a speed optimization that always sorts all independent tests to the front before looking at tests with dependencies. While this produces a technically correct execution order, it produces 'noise' by moving tests around more than necessary. The simplified resolver returns a more natural execution order:

#	Original order	after noisy resolver	after quiet resolver
1	A_independent	A_independent	A_independent
2	B_dep_on_A	C_independent	B_dep_on_A
3	C_independent	E_independent	C_independent
4	D_dep_on_C	B_dep_on_A	D_dep_on_C
5	E_independent	D_dep_on_C	E_independent

Changed functionality and impact

• no noticeable difference in performance or resource footprint
• no difference in configuration and input
• output is functionally unchanged, however the order might be slightly different; this only shows up using --debug or relying on an exact sequence of tests when logging

Software design and testing

• make dependency resolution optional again: 8fa2aff
• the TestSuiteSorter dependency resolver now is simpler and checks all tests at least once
• all interfaces between components stay the same
• add isolation tests for the TestSuiteSorter
• keep the current TextUI end-to-end tests