[pid_controller] Update tests

[Juliaj]

Main changes

• Follow up of [pid_controller] Fix logic for feedforward_mode with single reference interface #1520, added new test for two joints, two interfaces.
• Updated some of existing tests with additional test validation steps.

[codecov]

Codecov Report

Attention: Patch coverage is 89.85507% with 7 lines in your changes missing coverage. Please review.

Project coverage is 84.38%. Comparing base (c83cfb3) to head (9c0920c).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
pid_controller/src/pid_controller.cpp	58.82%	3 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1538      +/-   ##
==========================================
+ Coverage   84.27%   84.38%   +0.10%     
==========================================
  Files         123      124       +1     
  Lines       11359    11386      +27     
  Branches      961      959       -2     
==========================================
+ Hits         9573     9608      +35     
+ Misses       1470     1462       -8     
  Partials      316      316              

Flag	Coverage Δ
unittests	84.38% <89.85%> (+0.10%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
pid_controller/test/test_pid_controller.cpp	100.00% <100.00%> (ø)
pid_controller/test/test_pid_controller.hpp	84.78% <ø> (ø)
...roller/test/test_pid_controller_dual_interface.cpp	100.00% <100.00%> (ø)
pid_controller/src/pid_controller.cpp	72.03% <58.82%> (+3.61%)	⬆️

... and 4 files with indirect coverage changes

[christophfroehlich]

FYI: some of the changes are already included in #1437. I marked that ready for review now, as it got released and merged into ros2-testing.

[mergify]

This pull request is in conflict. Could you fix it @Juliaj?

[christophfroehlich]

Thx for adding more tests and the cleanup!

[christophfroehlich]

LGTM!
I just added a convenience function set_reference to TestablePidController, we have repeated that 10times already.