readTo('d', "abcd")
			for j := 0; j < 3; j++ {
				if err := r.UnreadByte(); err != nil {
					t.Fatalf("#%d: unexpected error on UnreadByte: %v", rno, err)
				}
				readTo('d', "d")
			}
			readTo('g', "efg")
		}

		// All data should have been read.
		_, err := r.ReadByte()
		if err != io.EOF {
			t.Errorf("#%d: got error %v; want EOF", rno, err)
		}
	}
}