Drupal\plugin\PluginDefinition\ArrayPluginDefinitionDecorator contains 1 abstract method and must therefore be declared abstract or implement the remaining methods

Not sure why the core issue went with id() instead of getId() but this should fix it, lets see if something else is broken too.

Core doesn't find classes directly in tests/src anymore, moved to Unit, it's only used there. Actually it is more common that those are directly in the test class file that needs it, but maybe more will need it at some point.

Between #2350807: add getId() and make id() a wrapper for it and deprecate it and #2246695: replace all core usages of id() with getid(), pretty sure Xano (or was it tstoeckler?) would want it the opposite direction.
But yes, this works too. RTBCing for now.

+++ b/src/PluginDefinition/PluginDefinitionInterface.php
@@ -26,6 +26,8 @@ interface PluginDefinitionInterface extends ComponentPluginDefinitionInterface {
+   * @deprecated Use ::id() instead.

missing in and when will be removed

Well yes, this is contrib, so I have no idea when it will be removed. 9.x-1.0? 8.x-3.0? Maybe before that we'll have semantic versions in contrib? Or maybe the referenced core issue will get in, which will turn this whole thing upside down anyway.

Honestly don't think we need to be so strict in contrib, maybe we should simply not deprecate anything yet, as we don't really know if id() or getId() will remain in the end.

Here's a version without the @deprecated.

+1, I think this is entirely reasonable to commit as-is, and leave the debate to another issue.

Thanks, committed!