If this is something only required for tests, it should be part of checkInputs.

But: this seems to build for me on current master, even without this PR.
It complains about which not available, but the tests still succeed.

I assume that failure on Hydra was caused by something else - further up in the logs, there's the following:

Not enough space left in /build (2600707200 KB) to decompress ./makeself-test.run (1 KB)
Use --nodiskspace option to skip this check and proceed anyway
Consider setting TMPDIR to a directory with more free space.
testQuiet:20:Failed

This seems to be a faulty comparison? 2600707200 clearly is greater than 1…

Digging further, there's also the following:

tail: invalid number of lines: '+'

gzip: stdin: unexpected end of file

I wonder if more is crashing here, but the test suite doesn't properly exit…

I agree that it should be part of checkInputs since it is only optionally required by extracttest:

https://github.com/megastep/makeself/search?q=which&unscoped_q=which

but since it is || returned there

https://github.com/megastep/makeself/blob/6a9d0e4e3598c897f7571ed5e5e6ca798727316f/test/extracttest#L42

it cannot cause the failure.

Maybe something to do with megastep/makeself#212

Weird. The comparison looks fine to me and has not been changed recently:

https://github.com/megastep/makeself/blame/1c2f8eb47e3bb1d895a3c7278319632fac6170bd/makeself-header.sh#L599

Adding which made it succeed at the first attempt, so I hope it wasn't just luck.