api test: update TestDefaulting

Logging and sub-tests were added to help debug this problem:
the test passes for ResourceClaim (same defaulting!) and fails
for the list, but only if run together with the other test cases?!

    $ go test ./pkg/api/testing
    --- FAIL: TestDefaulting (1.76s)
        --- FAIL: TestDefaulting/resource.k8s.io/v1alpha3,_Kind=ResourceClaimList (0.01s)
            defaulting_test.go:238: expected resource.k8s.io/v1alpha3, Kind=ResourceClaimList to trigger defaulting due to fuzzing
    FAIL
    FAIL	k8s.io/kubernetes/pkg/api/testing	17.294s
    FAIL
    $ go test -run=TestDefaulting/resource.k8s.io/v1alpha3,_Kind=ResourceClaimList ./pkg/api/testing
    ok  	k8s.io/kubernetes/pkg/api/testing	0.062s

What fixed that problem was increasing the likelihood of generating the right
test object by iterating more often before giving up.

pkg/api/testing/defaulting_test.go

@@ -192,6 +192,21 @@ func TestDefaulting(t *testing.T) {
 		{Group: "flowcontrol.apiserver.k8s.io", Version: "v1", Kind: "PriorityLevelConfigurationList"}:             {},
 	}
 
+	scheme := legacyscheme.Scheme
+	var testTypes orderedGroupVersionKinds
+	for gvk := range scheme.AllKnownTypes() {
+		if gvk.Version == runtime.APIVersionInternal {
+			continue
+		}
+		testTypes = append(testTypes, gvk)
+	}
+	sort.Sort(testTypes)
+
+	for _, gvk := range testTypes {
+		gvk := gvk
+		t.Run(gvk.String(), func(t *testing.T) {
+			// Each sub-tests gets its own fuzzer instance to make running it independent
+			// from what other tests ran before.
 			f := fuzz.New().NilChance(.5).NumElements(1, 1).RandSource(rand.NewSource(1))
 			f.Funcs(
 				func(s *runtime.RawExtension, c fuzz.Continue) {},
@@ -210,17 +225,6 @@ func TestDefaulting(t *testing.T) {
 				},
 			)
 
-	scheme := legacyscheme.Scheme
-	var testTypes orderedGroupVersionKinds
-	for gvk := range scheme.AllKnownTypes() {
-		if gvk.Version == runtime.APIVersionInternal {
-			continue
-		}
-		testTypes = append(testTypes, gvk)
-	}
-	sort.Sort(testTypes)
-
-	for _, gvk := range testTypes {
 			_, expectedChanged := typesWithDefaulting[gvk]
 			iter := 0
 			changedOnce := false
@@ -229,7 +233,11 @@ func TestDefaulting(t *testing.T) {
 					if !expectedChanged || changedOnce {
 						break
 					}
-				if iter > 300 {
+					// This uses to be 300, but for ResourceClaimList that was not high enough
+					// because depending on the starting conditions, the fuzzer never created the
+					// one combination where defaulting kicked in (empty string in non-empty slice
+					// in another non-empty slice).
+					if iter > 3000 {
 						t.Errorf("expected %s to trigger defaulting due to fuzzing", gvk)
 						break
 					}
@@ -250,16 +258,22 @@ func TestDefaulting(t *testing.T) {
 
 				// get internal
 				withDefaults := src.DeepCopyObject()
-			scheme.Default(withDefaults.(runtime.Object))
+				scheme.Default(withDefaults)
 
 				if !reflect.DeepEqual(original, withDefaults) {
+					diff := cmp.Diff(original, withDefaults)
+					if !changedOnce {
+						t.Logf("got diff (-fuzzed, +with defaults):\n%s", diff)
 						changedOnce = true
+					}
 					if !expectedChanged {
-					t.Errorf("{Group: \"%s\", Version: \"%s\", Kind: \"%s\"} did not expect defaults to be set - update expected or check defaulter registering: %s", gvk.Group, gvk.Version, gvk.Kind, cmp.Diff(original, withDefaults))
+						t.Errorf("{Group: \"%s\", Version: \"%s\", Kind: \"%s\"} did not expect defaults to be set - update expected or check defaulter registering: %s", gvk.Group, gvk.Version, gvk.Kind, diff)
 					}
 				}
 			}
+		})
 	}
+
 }
 
 func BenchmarkPodDefaulting(b *testing.B) {