Poking around

addon/addon-test-support/@ember/test-helpers/-internal/build-registry.ts

@@ -7,13 +7,16 @@ import require, { has } from 'require';
 import Ember from 'ember';
 
 import type { FullName } from '@ember/owner';
+import type Owner from '@ember/owner';
 
 // These shenanigans work around the fact that the import locations are not
 // public API and are not stable, so we jump through hoops to get the right
 // types and values to use.
 import {
   ContainerProxyMixin,
   RegistryProxyMixin,
+  type _RegistryProxyMixin,
+  type _ContainerProxyMixin,
 } from './-owner-mixin-imports';
 
 /**
@@ -53,7 +56,6 @@ function exposeRegistryMethodsWithoutDeprecations(container: any) {
 // NOTE: this is the same as what `EngineInstance`/`ApplicationInstance`
 // implement, and is thus a superset of the `InternalOwner` contract from Ember
 // itself.
-interface Owner extends RegistryProxyMixin, ContainerProxyMixin {}
 const Owner = EmberObject.extend(RegistryProxyMixin, ContainerProxyMixin, {
   _emberTestHelpersMockOwner: true,