Make filesys walk work.

api/krusty/kustomizer_test.go

@@ -11,14 +11,19 @@ import (
 	"sigs.k8s.io/kustomize/api/krusty"
 )
 
-func TestSomething1(t *testing.T) {
+// TODO: move most of the tests in api/internal/target
+// to this package, as they are all high level tests and
+// examples appropriate to this level and package.
+// The following test isn't much more than a usage example;
+// everything is actually tested down in api/internal/target.
+func TestSomething(t *testing.T) {
 	fSys := filesys.MakeFsInMemory()
 	b := krusty.MakeKustomizer(fSys, krusty.MakeDefaultOptions())
-	_, err := b.Run("hey")
+	_, err := b.Run("noSuchThing")
 	if err == nil {
 		t.Fatalf("expected error")
 	}
-	if err.Error() != "got file 'hey', but 'hey' must be a directory to be a root" {
+	if err.Error() != "'noSuchThing' doesn't exist" {
 		t.Fatalf("unexpected error: %v", err)
 	}
 }