~snip~
Sure, but if you have it already and need a bunch of testnet BTC, it should work nicely. I will try on the weekend with some modern desktop general-purpose hardware that I can access. I was surprised to see a >100MH/s hashrate on CPUs, since yours only managed single digits. Therefore, I was about to call this guide half-failed (the CPU part), but those benchmarks give me hope.
CPU mining absolutely works for testnet with relatively new devices.
Just did a quick benchmark with bfgminer on a mac mini M1(2020 device) with CPU only(you can also use OpenCL to use the GPU), and in less than 5 minutes I got 2 shares over Diff 1:
[XXX-XX-XX XX:12:17] New best share: 1
[XXX-XX-XX XX:12:17] Accepted fe912210 CPU 7 Diff 1/1
[XXX-XX-XX XX:12:21] 20s: 8.46 avg: 8.56 u:30.08 Mh/s | A:1 R:0+0(none) HW:0/none
[XXX-XX-XX XX:12:42] 20s: 8.61 avg: 8.60 u:26.34 Mh/s | A:1 R:0+0(none) HW:0/none
[XXX-XX-XX XX:13:02] 20s: 8.57 avg: 8.59 u:23.44 Mh/s | A:1 R:0+0(none) HW:0/none
[XXX-XX-XX XX:13:22] 20s: 8.59 avg: 8.59 u:21.09 Mh/s | A:1 R:0+0(none) HW:0/none
[XXX-XX-XX XX:13:43] 20s: 8.69 avg: 8.61 u:19.17 Mh/s | A:1 R:0+0(none) HW:0/none
[XXX-XX-XX XX:14:03] 20s: 8.73 avg: 8.63 u:17.58 Mh/s | A:1 R:0+0(none) HW:0/none
[XXX-XX-XX XX:14:23] 20s: 8.64 avg: 8.62 u:16.23 Mh/s | A:1 R:0+0(none) HW:0/none
[XXX-XX-XX XX:14:44] 20s: 8.70 avg: 8.63 u:15.07 Mh/s | A:1 R:0+0(none) HW:0/none
[XXX-XX-XX XX:15:04] 20s: 8.74 avg: 8.64 u:14.07 Mh/s | A:1 R:0+0(none) HW:0/none
[XXX-XX-XX XX:15:24] 20s: 8.71 avg: 8.64 u:13.19 Mh/s | A:1 R:0+0(none) HW:0/none
[XXX-XX-XX XX:15:44] 20s: 8.56 avg: 8.62 u:12.42 Mh/s | A:1 R:0+0(none) HW:0/none
[XXX-XX-XX XX:15:53] New best share: 291
[XXX-XX-XX XX:15:53] Accepted 00e0a123 CPU 5 Diff 291/1
You can see that it is absolutely possible to find a block when Diff is 1 with a CPU. It's just that it's way less probable than with an ASIC.
If you want to test a device without having to setup a local Bitcoin Core, you can do this:
./bfgminer -S cpu:auto --benchmark-intense
Also, notice the M1 hashrate hovering around 20Mh/s or so. It should be higher than that because I did the benchmark while using the device at 100% for other intensive tasks that I didn't want to stop.