Add a lister-gen expansion example

Signed-off-by: Stephen Kitt <skitt@redhat.com>

staging/src/k8s.io/code-generator/examples/apiserver/listers/example2/v1/expansion_generated.go

@@ -17,11 +17,3 @@ limitations under the License.
 // Code generated by lister-gen. DO NOT EDIT.
 
 package v1
-
-// TestTypeListerExpansion allows custom methods to be added to
-// TestTypeLister.
-type TestTypeListerExpansion interface{}
-
-// TestTypeNamespaceListerExpansion allows custom methods to be added to
-// TestTypeNamespaceLister.
-type TestTypeNamespaceListerExpansion interface{}

staging/src/k8s.io/code-generator/examples/apiserver/listers/example2/v1/testtype_expansion.go

@@ -0,0 +1,31 @@
+/*
+Copyright 2024 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package v1
+
+// TestTypeListerExpansion allows custom methods to be added to
+// TestTypeLister.
+type TestTypeListerExpansion interface {
+	CheckExpansionSupport()
+}
+
+// TestTypeNamespaceListerExpansion allows custom methods to be added to
+// TestTypeNamespaceLister.
+type TestTypeNamespaceListerExpansion interface{}
+
+func (*testTypeLister) CheckExpansionSupport() {
+	// This checks that lister-gen correctly supports expansions
+}