hi Russ,
Are you sure you have the proper kernel code loaded with the test firmware code that creates this sysfs file? Without that, this test will not work.
Nevertheless, the error message you reported in your first email indicates that the test_firmware device may not be present. Did you verify that the running system reports the expected configs? What does the following command show?
~# zgrep CONFIG_TEST_FIRMWARE /proc/config.gz CONFIG_TEST_FIRMWARE=y
best regards,