[release-0.22] 🐛Panic when trying to build more than one instance of fake.ClientBuilder (#3315)

* panic when trying to build more than one instance of fake.ClientBuilder Signed-off-by: Troy Connor <troy0820@users.noreply.github.com> * pr feedback Signed-off-by: Troy Connor <troy0820@users.noreply.github.com> --------- Signed-off-by: Troy Connor <troy0820@users.noreply.github.com> Co-authored-by: Troy Connor <troy0820@users.noreply.github.com>

Author: k8s-infra-cherrypick-robot

pkg/client/fake/client.go

@@ -141,6 +141,7 @@ type ClientBuilder struct {
 interceptorFuncs *interceptor.Funcs
 typeConverters []managedfields.TypeConverter
 returnManagedFields bool
+isBuilt bool
 
 // indexes maps each GroupVersionKind (GVK) to the indexes registered for that GVK.
 // The inner map maps from index name to IndexerFunc.
@@ -267,6 +268,9 @@ func (f *ClientBuilder) WithReturnManagedFields() *ClientBuilder {
 
 // Build builds and returns a new fake client.
 func (f *ClientBuilder) Build() client.WithWatch {
+if f.isBuilt {
+panic("Build() must not be called multiple times when creating a ClientBuilder")
+}
 if f.scheme == nil {
 f.scheme = scheme.Scheme
 }
@@ -344,6 +348,7 @@ func (f *ClientBuilder) Build() client.WithWatch {
 result = interceptor.NewClient(result, *f.interceptorFuncs)
 }
 
+f.isBuilt = true
 return result
 }
 

pkg/client/fake/client_test.go

@@ -3159,4 +3159,13 @@ var _ = Describe("Fake client builder", func() {
 Expect(err).NotTo(HaveOccurred())
 Expect(called).To(BeTrue())
 })
+
+It("should panic when calling build more than once", func() {
+cb := NewClientBuilder()
+anotherCb := cb
+cb.Build()
+Expect(func() {
+anotherCb.Build()
+}).To(Panic())
+})
 })