go/zodb: persistent tests: Factor checkObj out of TestPersistent

We are going to use this function in other tests too.

go/zodb/persistent_test.go

@@ -66,11 +66,10 @@ func init() {
 	RegisterClassAlias("t.zodb.MyOldObject", "t.zodb.MyObject")
 }
 
-func TestPersistent(t *testing.T) {
-	assert := require.New(t)
-
-	// checkObj verifies current state of persistent object.
-	checkObj := func(obj IPersistent, jar *Connection, oid Oid, serial Tid, state ObjectState, refcnt int32) {
+// checkObj verifies current state of persistent object.
+//
+// one can bind checkObj to t via tCheckObj.
+func checkObj(t testing.TB, obj IPersistent, jar *Connection, oid Oid, serial Tid, state ObjectState, refcnt int32) {
 	t.Helper()
 	xbase := reflect.ValueOf(obj).Elem().FieldByName("Persistent")
 	pbase := xbase.Addr().Interface().(*Persistent)
@@ -106,7 +105,20 @@ func TestPersistent(t *testing.T) {
 	if pbase.instance != obj {
 		badf("base.instance != obj")
 	}
+}
+
+// tCheckObj binds checkObj to t.
+func tCheckObj(t testing.TB) func(IPersistent, *Connection, Oid, Tid, ObjectState, int32) {
+	return func(obj IPersistent, jar *Connection, oid Oid, serial Tid, state ObjectState, refcnt int32) {
+		t.Helper()
+		checkObj(t, obj, jar, oid, serial, state, refcnt)
 	}
+}
+
+
+func TestPersistent(t *testing.T) {
+	assert := require.New(t)
+	checkObj := tCheckObj(t)
 
 	// unknown type -> Broken
 	xobj := newGhost("t.unknown", 10, nil)