You've probably realised this, but the failing tests for standards is because the new file tests/Drupal/good/GoodNamespace.php is not excluded when checking Coder's own files:

    <!-- Test files that should not be checked. -->
    <exclude-pattern>tests/*\.(inc|css|js|api\.php|tpl\.php)$</exclude-pattern>
    <exclude-pattern>tests/*/(good|bad)\.php$</exclude-pattern>
    <exclude-pattern>tests/*/drupal(6|7|8)/*\.php$</exclude-pattern>

The patterns above seem to exclude nearly all files in the tests/good/ folder but not everything. Am I right in thinking that all files in the tests/good folder should follow Drupal standards, and hence they are excluded because Coder uses a different customised set for it's own files? If so, we could exclude everything from tests/good in one statement, rather than try to cater for most files over the three patterns.

Sorry if this is wrong, I've not looked in great detail at what is not excluded from the above three.

Yep, this is not ready for review yet, was just uploading my work in progress here.

Sorry, yes of course. But I've done some learning in the meantime, I wanted to see if we could exclude everything in /good except the GoodUnitTest.php but I could not get a neagative pattern to work, so the easiest thing would be to add GoodNamespace into the tests/*/(good|GoodNamespace|bad)\.php$ pattern

Created upstream bug report at slevomat/coding-standard#1570

That bug was resolved, yay!

Now some test fails remain where Slevomat gets confused by multiple use statements, it somehow thinks one is a constant.

Not sure if we should simply drop this test case from Coder and not care about it anymore, or if we should try to improve the Slevomat sniff.

Reported the constant confusion upstream: slevomat/coding-standard#1581