I just came across an extension (BoilerPlate) that only required MW 1.32+ but uses the hook handler system, which wasn't introduced until 1.35. I sent a patch for that extension and the others I found with the same issue[1] but it would be useful to have a structure test

• check the minimum supported version of mediawiki
• check the rest of extension.json for trying to use features introduced in a specific version
  • HookHandlers -> 1.35
  • QUnitTestModule -> 1.33
  • manifest_version 2 -> 1.29
  • and many more, some listed at https://www.mediawiki.org/wiki/Manual:Extension.json/Schema

While an extension may be able to work in a version before the specific feature was introduced, it likely won't, or at least won't work as intended

[1] See https://gerrit.wikimedia.org/r/q/topic:%22hookhandlers-requires-1.35%22+(status:open%20OR%20status:merged)