}
		if len(ct.wantusrstr) != 0 && ct.wantusrstr != *ct.d.(*userDefinedString) {
			errf("want userDefined %q, got %q", ct.wantusrstr, *ct.d.(*userDefinedString))
		}
	}
}

func TestNullString(t *testing.T) {
	var ns NullString
	convertAssign(&ns, []byte("foo"))
	if !ns.Valid {
		t.Errorf("expecting not null")
	}
	if ns.String != "foo" {
		t.Errorf("expecting foo; got %q", ns.String)
	}

	}
}

// Test that a null for ,string is not replaced with the previous quoted string (issue 7046).
// It should also not be an error (issue 2540, issue 8587).
func TestNullString(t *testing.T) {
	type T struct {
		A int  `json:",string"`
		B int  `json:",string"`
		C *int `json:",string"`
	}
	data := []byte(`{"A": "1", "B": null, "C": null}`)
	var s T
	s.B = 1