testing/prototest: add extensions, unknown fields, typechecks

Change-Id: Ia9a7e0670f5f4655a564f9b5425fd63991c76960
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/183377
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
diff --git a/testing/prototest/prototest_test.go b/testing/prototest/prototest_test.go
index ec502c4..74ade17 100644
--- a/testing/prototest/prototest_test.go
+++ b/testing/prototest/prototest_test.go
@@ -22,9 +22,10 @@
 		(*testpb.TestRequired)(nil),
 		(*testpb.TestWeak)(nil),
 		(*irregularpb.Message)(nil),
+		(*testpb.TestAllExtensions)(nil),
 	} {
 		t.Run(fmt.Sprintf("%T", m), func(t *testing.T) {
-			prototest.TestMessage(t, m)
+			prototest.TestMessage(t, m, prototest.MessageOptions{})
 		})
 	}
 }