Improve test suite for FB_List

[ahuca]

1. Consider breaking down the current FB_List_Test test suite into multiple test suites each dedicated to testing a single method/property
2. Add more tests. Test ruthlessly, so that bugs like Fix bug with FB_List.RemoveAt #24 won't happen again

[ahuca]

Keep in mind not to overdo this for the whole project. FB_List is more complex and has many test cases hence it's more reasonable to split testing up into multiple test suites.