This behavior of `touch` is standardized in POSIX, so it should be available.
println "\n===> zstd created file timestamp tests"
datagen > tmp
-sleep 1 # could also use touch -t but I don't know how portable that is.
+touch -m -t 200001010000.00 tmp
println "test : copy mtime in file -> file compression "
zstd -f tmp -o tmp.zst
assertSameMTime tmp tmp.zst
-sleep 1 # could also use touch -t but I don't know how portable that is.
println "test : copy mtime in file -> file decompression "
zstd -f -d tmp.zst -o tmp.out
assertSameMTime tmp.zst tmp.out