Would this work, without having to use normaliseAddInput?:

Just gave it a go, but it seems ipfs.add is expecting an iterator:

TypeError: Cannot read property 'Symbol(Symbol.asyncIterator)' of undefined

We are able to get the job done if we turn the object into an async iterator

: (function * () {
   yield {
     content: getStdin(),
     mode: argv.mode,
     mtime
   }
 })()

Is there a iterator util for turning an element into a async iterator?

Weird, that should be supported. You should also be able to do:

: [{
     content: getStdin(),
     mode: argv.mode,
     mtime
   }]

That worked. Should I open a bug for the add function when passed:

{
   content: getStdin(),
   mode: argv.mode,
   mtime
}

I think this is because the test stubs ipfs.add to only return something when passed an iterable (async or otherwise) as the first argument:

ipfs.add.withArgs(matchIterable(), defaultAddArgs()).returns([{
  cid,
  path: 'readme'
}])

If you pass:

{
   content: getStdin(),
   mode: argv.mode,
   mtime
}

You're not passing an iterable so the stub doesn't match and undefined is returned from ipfs.add because JavaScript which causes the reported TypeError in the for await..of loop.

The test needs to be updated to this:

it('add from pipe with mtime=100', async () => {
  const cid = new CID('QmPZ9gcCEpqKTo6aq61g2nXGUhM4iCL3ewB6LDXZCtioEB')

  ipfs.add.withArgs(sinon.match({
    content: matchIterable(),
    mtime: { secs: 100 }
  }), defaultAddArgs()).returns([{
    cid,
    path: 'readme'
  }])

  const proc = cli('add --mtime=100', {
    ipfs,
    getStdin: function * () {
      yield Buffer.from('hello\n')
    }
  })

  const out = await proc
  expect(out).to.equal(`added ${cid} ${cid}\n`)

  const input = ipfs.add.getCall(0).args[0]
  expect(input).to.have.nested.property('mtime.secs', 100)
})

TBH it could even lose the last assertion (for the mtime.secs property) as it'll only fail if the ipfs.add stub doesn't match, which will cause the TypeError issue before it gets to that assertion.

@achingbrain I have updated the usage and test as suggested. The mocking had to be changed in 'add from pipe' as well.