Add PodSecurityContext and backward compatibility tests

pkg/api/testing/fuzzer.go

@@ -92,14 +92,18 @@ func FuzzerFor(t *testing.T, version string, src rand.Source) *fuzz.Fuzzer {
 			j.LabelSelector, _ = labels.Parse("a=b")
 			j.FieldSelector, _ = fields.ParseSelector("a=b")
 		},
-		func(j *api.PodSpec, c fuzz.Continue) {
-			c.FuzzNoCustom(j)
+		func(s *api.PodSpec, c fuzz.Continue) {
+			c.FuzzNoCustom(s)
 			// has a default value
 			ttl := int64(30)
 			if c.RandBool() {
 				ttl = int64(c.Uint32())
 			}
-			j.TerminationGracePeriodSeconds = &ttl
+			s.TerminationGracePeriodSeconds = &ttl
+
+			if s.SecurityContext == nil {
+				s.SecurityContext = &api.PodSecurityContext{}
+			}
 		},
 		func(j *api.PodPhase, c fuzz.Continue) {
 			statuses := []api.PodPhase{api.PodPending, api.PodRunning, api.PodFailed, api.PodUnknown}