recreateReadbackBuffer();

    debug("");
    debug("write-fence-delete-wait-read");
    gl.copyBufferSubData(gl.ARRAY_BUFFER, gl.COPY_WRITE_BUFFER, 0, 0, 8);
    deleteReadbackBuffer();
    await fence();
    checkGetBufferSubData(gl.INVALID_OPERATION, "noData");
    recreateReadbackBuffer();

    // crbug.com/941930
    {
        debug("");
        debug("write-delete-recreate-fence-wait-read");
        gl.copyBufferSubData(gl.COPY_READ_BUFFER, gl.COPY_WRITE_BUFFER, 0, 0, 8);
        deleteReadbackBuffer(