When a cursor returns a single document in the firstBatch and the cursor is exhausted, we do not clean the cursor up.  The following test demonstrates this behavior:

it.only('should close the cursor when there are no documents remaining', async function () {    

  await client.connect();
  await client.db('foo')
    .collection('bar')
    .insertOne({ name: 'bailey' });
  const cursor = client.db('foo')
    .collection('bar')
    .find({});    
  cursor.limit(1);    
  cursor.batchSize(-1);
  const doc = await cursor.next();
    
  expect(doc, 'expected a result but none was received').to.exist;
  expect(
    cursor.closed, 
    'expected cursor to be closed but it was not'
    ).to.be.true;  
}); 

Root Cause

In abstract_cursor.ts' next method, if the cursor is not initialized, we:

• initialize the cursor
• return the first document

After returning the first document, we don't check if the cursor is exhausted and close it if it is.

Unknowns

Is this a bug or works as designed?  We tell users they must always close their cursors, so we could demand that users iterate their cursors until they're complete (another call to `next` will close the cursor in the above test).  However, in `findOne` we construct a cursor and immediately return the result of a single document cursor without closing it.  So we either need to fix the bug outlined in this ticket, or ensure we close the cursor we're creating in `findOne`.

AC

Implementation

• Add handling for cursor exhaustion upon firstBatch, if id == 0, cleanup.

Testing

• closes the cursor if it is exhausted on the firstBatch