b := w.AvailableBuffer()
		if w.Available() != cap(b) {
			t.Fatalf("Available() = %v, want %v", w.Available(), cap(b))
		}

		// While not recommended, it is valid to append to a shifted buffer.
		// This forces Write to copy the input.
		if rn.Intn(8) == 0 && cap(b) > 0 {
			b = b[1:1:cap(b)]
		}

		// Append a random integer of varying width.
		n := int64(rn.Intn(1 << rn.Intn(30)))