Sinon test error with whois-json

Question

I have a service API which up until recently used the whois library to get data. I use sinon to test the API:

const mockWhoisLookup = sinon.mock(whois);
mockWhoisLookup
  .expects('lookup')
  .once()
  .withArgs('deals.dk')
  .callsFake((domain, callback) => {
    callback(undefined, whoisSampleResponse);
  });

I've decided to use whois-json instead as it provides a 'cleaner' output. The issue is that when I now run the test it gives me an error output:

TypeError: Attempted to wrap undefined property lookup as function

  61 |     const mockWhoisLookup = sinon.mock(whois);
  62 |     mockWhoisLookup
> 63 |       .expects('lookup')
  64 |       .once()
  65 |       .withArgs('deals.dk')
  66 |       .callsFake((domain, callback) => {

How do I solve this issue?