For GBA, the quick-n-dirty:
Start it and look at the manual.
You can check by extracting the rom and comparing the rom's ID with the alldata filename.
inject_gba -v --inpsb=/path/to/your/alldata.psb.m --outrom=extracted.gba
xxd -s 0xAC -l 6 extracted.gba
Which will print something like this:
$ inject_gba -v --inpsb content/alldata.psb.m --outrom extracted.gba
Reading 'content/alldata.psb.m'
Reading file content/alldata.bin
Writing 'extracted.gba'
Extracting 'system/roms/AAFFE0.128.m'
^^ This shows the original name, I don't patch that when injecting.
$ xxd -s 0xAC -l 6 extracted.gba
000000ac: 4146 4645 3038 AFFE08
^^ This shows what the rom is. If it was injected, it will almost certainly differ.