Take postcodes and get the Lat long information from them
Test case structure
It doesn't seem like the code totally &quot;lacked effort and structure&quot; but the structure, at least of the test cases, could be better. Since all three describe() blocks contain a test that calls getLatlonFromPostcode so there could be a single describe() block with three it() blocks to test the various aspects of how the function should handle given postcodes.
Utilizing await
One of the main benefits of using await is to eliminate the need for callbacks to .then(). Some code utilizes this benefit e.g. the test functions but the methods in app.js do not - e.g.

await getLatlonFromPostcode(postcode).then((data) =&gt; {
  res.send(data);
});


Ideally, the res.send() call would be on a sequential line instead of in a .then() callback function:
const data = await getLatlonFromPostcode(postcode);
res.send(data);

Or even simpler:
res.send(await getLatlonFromPostcode(postcode));

Error handling
As an interviewer I would be checking to see how well the code handles edge cases. Obviously with promises comes rejection. The first couple methods don't appear to handle rejected promises at all.
Import Star
The two import statements import everything from the modules being imported. In the Airbnb style guide, it recommends no wildcards:

Why? This makes sure you have a single default export.1

The import for axios could be simplified using destructuring assignment:
import { get, post} from &quot;axios&quot;;

That way the code can call get() and post() without needing to reference axios, and the other items exported from axios that are not needed are not imported.