@@ -540,6 +540,9 @@ describe('Aggregation', function() {
             expect(result._id.tags).to.equal('good');
             expect(result.authors).to.eql(['bob']);
 
+            // Since cursor will not be "exhausted", since batchSize is 1,
+            // we need to manually call close on the cursor
+            cursor.close();
             client.close();
             done();
           });
'use strict';
var expect = require('chai').expect;

describe('Aggregation', function() {
  /**
   * Correctly call the aggregation framework using a pipeline in an Array.
   *
   * @example-class Collection
   * @example-method aggregate
   * @ignore
   */
  it('should correctly execute simple aggregation pipeline using array', {
    // Add a tag that our runner can trigger on
    // in this case we are setting that node needs to be higher than 0.10.X to run
    metadata: {
      requires: {
        mongodb: '>2.1.0',
        topology: ['single', 'replicaset', 'sharded', 'ssl', 'heap', 'wiredtiger']
      }
    },

    // The actual test we wish to run
    test: function(done) {
      var client = this.configuration.newClient({ w: 1 }, { poolSize: 1 }),
        databaseName = this.configuration.db;

      // LINE var MongoClient = require('mongodb').MongoClient;
      // LINE MongoClient.connect('mongodb://localhost:27017/test', function(err, db) {
      // REPLACE this.configuration.writeConcernMax() WITH {w:1}
      // REMOVE-LINE test.
      // BEGIN
      client.connect(function(err, client) {
        expect(err).to.be.null;

        var db = client.db(databaseName);
        // Some docs for insertion
        var docs = [
          {
            title: 'this is my title',
            author: 'bob',
            posted: new Date(),
            pageViews: 5,
            tags: ['fun', 'good', 'fun'],
            other: { foo: 5 },
            comments: [
              { author: 'joe', text: 'this is cool' },
              { author: 'sam', text: 'this is bad' }
            ]
          }
        ];

        // Create a collection
        var collection = db.collection('shouldCorrectlyExecuteSimpleAggregationPipelineUsingArray');
        // Insert the docs
        collection.insert(docs, { w: 1 }, function(err, result) {
          expect(result).to.exist;
          expect(err).to.be.null;

          // Execute aggregate, notice the pipeline is expressed as an Array
          collection.aggregate(
            [
              {
                $project: {
                  author: 1,
                  tags: 1
                }
              },
              { $unwind: '$tags' },
              {
                $group: {
                  _id: { tags: '$tags' },
                  authors: { $addToSet: '$author' }
                }
              }
            ],
            function(err, cursor) {
              expect(err).to.be.null;

              cursor.toArray(function(err, result) {
                expect(err).to.be.null;
                expect(result[0]._id.tags).to.equal('good');
                expect(result[0].authors).to.eql(['bob']);
                expect(result[1]._id.tags).to.equal('fun');
                expect(result[1].authors).to.eql(['bob']);

                client.close();
                done();
              });
            }
          );
        });
      });
      // END
    }
  });

  /**
   * Correctly call the aggregation framework using a pipeline expressed as an argument list.
   *
   * @example-class Collection
   * @example-method aggregate
   * @ignore
   */
  it('should fail when executing simple aggregation pipeline using arguments not an array', {
    // Add a tag that our runner can trigger on
    // in this case we are setting that node needs to be higher than 0.10.X to run
    metadata: {
      requires: {
        mongodb: '>2.1.0',
        topology: ['single', 'replicaset', 'sharded', 'ssl', 'heap', 'wiredtiger']
      }
    },

    // The actual test we wish to run
    test: function(done) {
      var client = this.configuration.newClient({ w: 1 }, { poolSize: 1 }),
        databaseName = this.configuration.db;

      // LINE var MongoClient = require('mongodb').MongoClient;
      // LINE MongoClient.connect('mongodb://localhost:27017/test', function(err, db) {
      // REPLACE this.configuration.writeConcernMax() WITH {w:1}
      // REMOVE-LINE test.
      // BEGIN
      client.connect(function(err, client) {
        expect(err).to.be.null;

        var db = client.db(databaseName);
        // Some docs for insertion
        var docs = [
          {
            title: 'this is my title',
            author: 'bob',
            posted: new Date(),
            pageViews: 5,
            tags: ['fun', 'good', 'fun'],
            other: { foo: 5 },
            comments: [
              { author: 'joe', text: 'this is cool' },
              { author: 'sam', text: 'this is bad' }
            ]
          }
        ];

        // Create a collection
        var collection = db.collection(
          'shouldCorrectlyExecuteSimpleAggregationPipelineUsingArguments'
        );
        // Insert the docs
        collection.insert(docs, { w: 1 }, function(err, result) {
          expect(result).to.exist;
          expect(err).to.be.null;

          // Execute aggregate, notice the pipeline is expressed as function call parameters
          // instead of an Array.
          collection.aggregate(
            {
              $project: {
                author: 1,
                tags: 1
              }
            },
            { $unwind: '$tags' },
            {
              $group: {
                _id: { tags: '$tags' },
                authors: { $addToSet: '$author' }
              }
            },
            function(err, cursor) {
              expect(err).to.be.null;

              cursor.toArray(function(err, result) {
                expect(err).to.be.null;
                expect(result[0]._id.tags).to.equal('good');
                expect(result[0].authors).to.eql(['bob']);
                expect(result[1]._id.tags).to.equal('fun');
                expect(result[1].authors).to.eql(['bob']);

                client.close();
                done();
              });
            }
          );
        });
      });
      // END
    }
  });

  /**
   * Correctly call the aggregation framework using a pipeline expressed as an argument list.
   *
   * @example-class Collection
   * @example-method aggregate
   * @ignore
   */
  it('should fail when executing simple aggregation pipeline using arguments using single object', {
    // Add a tag that our runner can trigger on
    // in this case we are setting that node needs to be higher than 0.10.X to run
    metadata: {
      requires: {
        mongodb: '>2.1.0',
        topology: ['single', 'replicaset', 'sharded', 'ssl', 'heap', 'wiredtiger']
      }
    },

    // The actual test we wish to run
    test: function(done) {
      var client = this.configuration.newClient({ w: 1 }, { poolSize: 1 }),
        databaseName = this.configuration.db;

      // LINE var MongoClient = require('mongodb').MongoClient;
      // LINE MongoClient.connect('mongodb://localhost:27017/test', function(err, db) {
      // REPLACE this.configuration.writeConcernMax() WITH {w:1}
      // REMOVE-LINE test.
      // BEGIN
      client.connect(function(err, client) {
        expect(err).to.be.null;

        var db = client.db(databaseName);
        // Some docs for insertion
        var docs = [
          {
            title: 'this is my title',
            author: 'bob',
            posted: new Date(),
            pageViews: 5,
            tags: ['fun', 'good', 'fun'],
            other: { foo: 5 },
            comments: [
              { author: 'joe', text: 'this is cool' },
              { author: 'sam', text: 'this is bad' }
            ]
          }
        ];

        // Create a collection
        var collection = db.collection(
          'shouldCorrectlyExecuteSimpleAggregationPipelineUsingArguments'
        );
        // Insert the docs
        collection.insert(docs, { w: 1 }, function(err, result) {
          expect(result).to.exist;
          expect(err).to.be.null;

          // Execute aggregate, notice the pipeline is expressed as function call parameters
          // instead of an Array.
          collection.aggregate(
            {
              $project: {
                author: 1,
                tags: 1
              }
            },
            { $unwind: '$tags' },
            {
              $group: {
                _id: { tags: '$tags' },
                authors: { $addToSet: '$author' }
              }
            },
            function(err, cursor) {
              expect(err).to.be.null;

              cursor.toArray(function(err, result) {
                expect(err).to.be.null;
                expect(result[0]._id.tags).to.equal('good');
                expect(result[0].authors).to.eql(['bob']);
                expect(result[1]._id.tags).to.equal('fun');
                expect(result[1].authors).to.eql(['bob']);

                client.close();
                done();
              });
            }
          );
        });
      });
      // END
    }
  });

  /**
   * Correctly call the aggregation framework to return a cursor
   *
   * @example-class Collection
   * @example-method aggregate
   * @ignore
   */
  it('should correctly return and iterate over all the cursor results', {
    // Add a tag that our runner can trigger on
    // in this case we are setting that node needs to be higher than 0.10.X to run
    metadata: {
      requires: {
        mongodb: '>2.1.0',
        topology: 'single',
        node: '>0.10.0'
      }
    },

    // The actual test we wish to run
    test: function(done) {
      var client = this.configuration.newClient({ w: 1 }, { poolSize: 1 }),
        databaseName = this.configuration.db;

      // LINE var MongoClient = require('mongodb').MongoClient;
      // LINE MongoClient.connect('mongodb://localhost:27017/test', function(err, db) {
      // REPLACE this.configuration.writeConcernMax() WITH {w:1}
      // REMOVE-LINE test.
      // BEGIN
      client.connect(function(err, client) {
        expect(err).to.be.null;

        var db = client.db(databaseName);
        // Some docs for insertion
        var docs = [
          {
            title: 'this is my title',
            author: 'bob',
            posted: new Date(),
            pageViews: 5,
            tags: ['fun', 'good', 'fun'],
            other: { foo: 5 },
            comments: [
              { author: 'joe', text: 'this is cool' },
              { author: 'sam', text: 'this is bad' }
            ]
          }
        ];

        // Create a collection
        var collection = db.collection('shouldCorrectlyDoAggWithCursorGet');
        // Insert the docs
        collection.insert(docs, { w: 1 }, function(err, result) {
          expect(err).to.be.null;
          expect(result).to.exist;

          // Execute aggregate, notice the pipeline is expressed as an Array
          var cursor = collection.aggregate([
            {
              $project: {
                author: 1,
                tags: 1
              }
            },
            { $unwind: '$tags' },
            {
              $group: {
                _id: { tags: '$tags' },
                authors: { $addToSet: '$author' }
              }
            }
          ]);

          // Iterate over all the items in the cursor
          cursor.toArray(function(err, result) {
            expect(err).to.be.null;
            expect(result).to.exist;

            client.close();
            done();
          });
        });
      });
      // END
    }
  });

  /**
   * Correctly call the aggregation framework to return a cursor and call explain
   *
   * @example-class Collection
   * @example-method aggregate
   * @ignore
   */
  it('should correctly return a cursor and call explain', {
    // Add a tag that our runner can trigger on
    // in this case we are setting that node needs to be higher than 0.10.X to run
    metadata: {
      requires: {
        mongodb: '>2.5.3',
        topology: 'single',
        node: '>0.10.0'
      }
    },

    // The actual test we wish to run
    test: function(done) {
      var client = this.configuration.newClient({ w: 1 }, { poolSize: 1 }),
        databaseName = this.configuration.db;

      // LINE var MongoClient = require('mongodb').MongoClient;
      // LINE MongoClient.connect('mongodb://localhost:27017/test', function(err, db) {
      // REPLACE this.configuration.writeConcernMax() WITH {w:1}
      // REMOVE-LINE test.
      // BEGIN
      client.connect(function(err, client) {
        expect(err).to.be.null;

        var db = client.db(databaseName);
        // Some docs for insertion
        var docs = [
          {
            title: 'this is my title',
            author: 'bob',
            posted: new Date(),
            pageViews: 5,
            tags: ['fun', 'good', 'fun'],
            other: { foo: 5 },
            comments: [
              { author: 'joe', text: 'this is cool' },
              { author: 'sam', text: 'this is bad' }
            ]
          }
        ];

        // Create a collection
        var collection = db.collection('shouldCorrectlyDoAggWithCursorGet');
        // Insert the docs
        collection.insert(docs, { w: 1 }, function(err, result) {
          expect(result).to.exist;
          expect(err).to.be.null;

          // Execute aggregate, notice the pipeline is expressed as an Array
          var cursor = collection.aggregate(
            [
              {
                $project: {
                  author: 1,
                  tags: 1
                }
              },
              { $unwind: '$tags' },
              {
                $group: {
                  _id: { tags: '$tags' },
                  authors: { $addToSet: '$author' }
                }
              }
            ],
            {
              cursor: { batchSize: 100 }
            }
          );

          // Iterate over all the items in the cursor
          cursor.explain(function(err, result) {
            expect(err).to.be.null;
            expect(result.stages).to.have.length(4);

            client.close();
            done();
          });
        });
      });
      // END
    }
  });

  /**
   * Correctly call the aggregation framework to return a cursor with batchSize 1 and get the first result using next
   *
   * @example-class Collection
   * @example-method aggregate
   * @ignore
   */
  it('should correctly return a cursor with batchSize 1 and call next', {
    // Add a tag that our runner can trigger on
    // in this case we are setting that node needs to be higher than 0.10.X to run
    metadata: {
      requires: {
        mongodb: '>2.5.3',
        topology: 'single',
        node: '>0.10.0'
      }
    },

    // The actual test we wish to run
    test: function(done) {
      var client = this.configuration.newClient({ w: 1 }, { poolSize: 1 }),
        databaseName = this.configuration.db;

      // LINE var MongoClient = require('mongodb').MongoClient;
      // LINE MongoClient.connect('mongodb://localhost:27017/test', function(err, db) {
      // REPLACE this.configuration.writeConcernMax() WITH {w:1}
      // REMOVE-LINE test.
      // BEGIN
      client.connect(function(err, client) {
        expect(err).to.be.null;

        var db = client.db(databaseName);
        // Some docs for insertion
        var docs = [
          {
            title: 'this is my title',
            author: 'bob',
            posted: new Date(),
            pageViews: 5,
            tags: ['fun', 'good', 'fun'],
            other: { foo: 5 },
            comments: [
              { author: 'joe', text: 'this is cool' },
              { author: 'sam', text: 'this is bad' }
            ]
          }
        ];

        // Create a collection
        var collection = db.collection('shouldCorrectlyDoAggWithCursorGet');
        // Insert the docs
        collection.insert(docs, { w: 1 }, function(err, result) {
          expect(result).to.exist;
          expect(err).to.be.null;

          // Execute aggregate, notice the pipeline is expressed as an Array
          var cursor = collection.aggregate(
            [
              {
                $project: {
                  author: 1,
                  tags: 1
                }
              },
              { $unwind: '$tags' },
              {
                $group: {
                  _id: { tags: '$tags' },
                  authors: { $addToSet: '$author' }
                }
              }
            ],
            {
              cursor: { batchSize: 1 }
            }
          );

          // Iterate over all the items in the cursor
          cursor.next(function(err, result) {
            expect(err).to.be.null;
            expect(result._id.tags).to.equal('good');
            expect(result.authors).to.eql(['bob']);

            client.close();
            done();
          });
        });
      });
      // END
    }
  });

  /**
   * Correctly call the aggregation framework and write the results to a new collection
   *
   * @example-class Collection
   * @example-method aggregate
   * @ignore
   */
  it('should correctly write the results out to a new collection', {
    // Add a tag that our runner can trigger on
    // in this case we are setting that node needs to be higher than 0.10.X to run
    metadata: {
      requires: {
        mongodb: '>2.5.0',
        topology: ['single', 'replicaset', 'sharded', 'ssl', 'heap', 'wiredtiger']
      }
    },

    // The actual test we wish to run
    test: function(done) {
      var client = this.configuration.newClient({ w: 1 }, { poolSize: 1 }),
        databaseName = this.configuration.db;

      // LINE var MongoClient = require('mongodb').MongoClient;
      // LINE MongoClient.connect('mongodb://localhost:27017/test', function(err, db) {
      // REPLACE this.configuration.writeConcernMax() WITH {w:1}
      // REMOVE-LINE test.
      // BEGIN
      client.connect(function(err, client) {
        expect(err).to.be.null;

        var db = client.db(databaseName);
        // Some docs for insertion
        var docs = [
          {
            title: 'this is my title',
            author: 'bob',
            posted: new Date(),
            pageViews: 5,
            tags: ['fun', 'good', 'fun'],
            other: { foo: 5 },
            comments: [
              { author: 'joe', text: 'this is cool' },
              { author: 'sam', text: 'this is bad' }
            ]
          }
        ];

        // Create a collection
        var collection = db.collection('shouldCorrectlyDoAggWithCursorGet');
        // Insert the docs
        collection.insert(docs, { w: 1 }, function(err, result) {
          expect(result).to.exist;
          expect(err).to.be.null;

          // Execute aggregate, notice the pipeline is expressed as an Array
          collection.aggregate(
            [
              {
                $project: {
                  author: 1,
                  tags: 1
                }
              },
              { $unwind: '$tags' },
              {
                $group: {
                  _id: { tags: '$tags' },
                  authors: { $addToSet: '$author' }
                }
              }
            ],
            {
              out: 'testingOutCollectionForAggregation'
            },
            function(err, cursor) {
              expect(err).to.be.null;

              cursor.toArray(function(err, results) {
                expect(err).to.be.null;
                expect(results).to.be.empty;

                client.close();
                done();
              });
            }
          );
        });
      });
      // END
    }
  });

  /**
   * Correctly use allowDiskUse when performing an aggregation
   *
   * @example-class Collection
   * @example-method aggregate
   * @ignore
   */
  it('should correctly use allowDiskUse when performing an aggregation', {
    // Add a tag that our runner can trigger on
    // in this case we are setting that node needs to be higher than 0.10.X to run
    metadata: {
      requires: {
        mongodb: '>2.5.5',
        topology: ['single', 'replicaset', 'sharded', 'ssl', 'heap', 'wiredtiger']
      }
    },

    // The actual test we wish to run
    test: function(done) {
      var client = this.configuration.newClient({ w: 1 }, { poolSize: 1 }),
        databaseName = this.configuration.db;

      // LINE var MongoClient = require('mongodb').MongoClient;
      // LINE MongoClient.connect('mongodb://localhost:27017/test', function(err, db) {
      // REPLACE this.configuration.writeConcernMax() WITH {w:1}
      // REMOVE-LINE test.
      // BEGIN
      client.connect(function(err, client) {
        expect(err).to.be.null;

        var db = client.db(databaseName);
        // Some docs for insertion
        var docs = [
          {
            title: 'this is my title',
            author: 'bob',
            posted: new Date(),
            pageViews: 5,
            tags: ['fun', 'good', 'fun'],
            other: { foo: 5 },
            comments: [
              { author: 'joe', text: 'this is cool' },
              { author: 'sam', text: 'this is bad' }
            ]
          }
        ];

        // Create a collection
        var collection = db.collection('shouldCorrectlyDoAggWithCursorGet');
        // Insert the docs
        collection.insert(docs, { w: 1 }, function(err, result) {
          expect(result).to.exist;
          expect(err).to.be.null;

          // Execute aggregate, notice the pipeline is expressed as an Array
          collection.aggregate(
            [
              {
                $project: {
                  author: 1,
                  tags: 1
                }
              },
              { $unwind: '$tags' },
              {
                $group: {
                  _id: { tags: '$tags' },
                  authors: { $addToSet: '$author' }
                }
              }
            ],
            {
              allowDiskUse: true
            },
            function(err, cursor) {
              expect(err).to.be.null;

              cursor.toArray(function(err, results) {
                expect(err).to.be.null;
                expect(results[0]._id.tags).to.equal('good');
                expect(results[0].authors).to.eql(['bob']);
                expect(results[1]._id.tags).to.equal('fun');
                expect(results[1].authors).to.eql(['bob']);

                client.close();
                done();
              });
            }
          );
        });
      });
      // END
    }
  });

  /**
   * Correctly perform simple group
   * @ignore
   */
  it('should perform a simple group aggregation', {
    // Add a tag that our runner can trigger on
    // in this case we are setting that node needs to be higher than 0.10.X to run
    metadata: {
      requires: {
        mongodb: '>2.5.5',
        topology: ['single', 'replicaset', 'sharded', 'ssl', 'heap', 'wiredtiger']
      }
    },

    // The actual test we wish to run
    test: function(done) {
      var databaseName = this.configuration.db;
      var client = this.configuration.newClient(this.configuration.writeConcernMax(), {
        poolSize: 1
      });

      client.connect(function(err, client) {
        expect(err).to.be.null;

        var db = client.db(databaseName);
        // Create a collection
        var col = db.collection('shouldPerformSimpleGroupAggregation');
        col.remove({}, function(err) {
          expect(err).to.be.null;

          // Insert a single document
          col.insert([{ a: 1 }, { a: 1 }, { a: 1 }], function(err, r) {
            expect(err).to.be.null;
            expect(r.result.n).to.equal(3);

            // Get first two documents that match the query
            col
              .aggregate([
                { $match: {} },
                {
                  $group: { _id: '$a', total: { $sum: '$a' } }
                }
              ])
              .toArray(function(err, docs) {
                expect(err).to.be.null;
                expect(docs[0].total).to.equal(3);

                client.close();
                done();
              });
          });
        });
      });
    }
  });

  /**
   * Correctly perform simple group
   * @ignore
   */
  it('should correctly perform an aggregation using a collection name with dot in it', {
    // Add a tag that our runner can trigger on
    // in this case we are setting that node needs to be higher than 0.10.X to run
    metadata: {
      requires: {
        mongodb: '>2.5.5',
        topology: ['single', 'replicaset', 'sharded', 'ssl', 'heap', 'wiredtiger']
      }
    },

    // The actual test we wish to run
    test: function(done) {
      var databaseName = this.configuration.db;
      var client = this.configuration.newClient(this.configuration.writeConcernMax(), {
        poolSize: 1
      });

      client.connect(function(err, client) {
        expect(err).to.be.null;

        var db = client.db(databaseName);
        db.collection('te.st', function(err, col) {
          expect(err).to.be.null;
          var count = 0;

          col.insert([{ a: 1 }, { a: 1 }, { a: 1 }], function(err, r) {
            expect(err).to.be.null;
            expect(r.result.n).to.equal(3);

            //Using callback - OK
            col.aggregate([{ $project: { a: 1 } }], function(err, cursor) {
              expect(err).to.be.null;

              cursor.toArray(function(err, docs) {
                expect(err).to.be.null;
                expect(docs.length).to.be.greaterThan(0);

                //Using cursor - KO
                col
                  .aggregate([{ $project: { a: 1 } }], {
                    cursor: { batchSize: 10000 }
                  })
                  .forEach(
                    function() {
                      count = count + 1;
                    },
                    function(err) {
                      expect(err).to.be.null;
                      expect(count).to.be.greaterThan(0);

                      client.close();
                      done();
                    }
                  );
              });
            });
          });
        });
      });
    }
  });

  /**
   * Correctly call the aggregation framework to return a cursor with batchSize 1 and get the first result using next
   *
   * @ignore
   */
  it('should fail aggregation due to illegal cursor option and streams', {
    // Add a tag that our runner can trigger on
    // in this case we are setting that node needs to be higher than 0.10.X to run
    metadata: {
      requires: {
        mongodb: '>2.5.3',
        topology: 'single',
        node: '>0.10.0'
      }
    },

    // The actual test we wish to run
    test: function(done) {
      var databaseName = this.configuration.db;
      var client = this.configuration.newClient(this.configuration.writeConcernMax(), {
        poolSize: 1
      });

      client.connect(function(err, client) {
        expect(err).to.be.null;

        var db = client.db(databaseName);
        // Some docs for insertion
        var docs = [
          {
            title: 'this is my title',
            author: 'bob',
            posted: new Date(),
            pageViews: 5,
            tags: ['fun', 'good', 'fun'],
            other: { foo: 5 },
            comments: [
              { author: 'joe', text: 'this is cool' },
              { author: 'sam', text: 'this is bad' }
            ]
          }
        ];

        // Create a collection
        var collection = db.collection('shouldCorrectlyDoAggWithCursorGetStream');
        // Insert the docs
        collection.insert(docs, { w: 1 }, function(err, result) {
          expect(result).to.exist;
          expect(err).to.be.null;

          try {
            // Execute aggregate, notice the pipeline is expressed as an Array
            collection.aggregate(
              [
                {
                  $project: {
                    author: 1,
                    tags: 1
                  }
                },
                { $unwind: '$tags' },
                {
                  $group: {
                    _id: { tags: '$tags' },
                    authors: { $addToSet: '$author' }
                  }
                }
              ],
              {
                cursor: 1
              }
            );
          } catch (err) {
            client.close();
            return done();
          }

          // should never happen
          expect(true).to.be.false;
        });
      });
    }
  });

  it('should fail if you try to use explain flag with readConcern/writeConcern', {
    metadata: {
      requires: {
        mongodb: '>3.6.0',
        topology: 'single'
      }
    },

    test: function(done) {
      var databaseName = this.configuration.db;
      var client = this.configuration.newClient(this.configuration.writeConcernMax(), {
        poolSize: 1
      });

      const testCases = [
        { readConcern: { level: 'local' } },
        { writeConcern: { j: true } },
        { readConcern: { level: 'local' }, writeConcern: { j: true } }
      ];

      client.connect(function(err, client) {
        const wrapup = err => {
          client.close();
          done(err);
        };

        const db = client.db(databaseName);

        Promise.all(
          testCases.map(testCase => {
            const stringifiedTestCase = JSON.stringify(testCase);
            const collection = db.collection('foo');
            Object.assign(collection.s, testCase);
            try {
              const promise = collection
                .aggregate([{ $project: { _id: 0 } }, { $out: 'bar' }], { explain: true })
                .toArray()
                .then(
                  () => {
                    throw new Error(
                      'Expected aggregation to not succeed for options ' + stringifiedTestCase
                    );
                  },
                  () => {
                    throw new Error(
                      'Expected aggregation to fail on client instead of server for options ' +
                        stringifiedTestCase
                    );
                  }
                );

              return promise;
            } catch (e) {
              expect(e).to.exist;
              return Promise.resolve();
            }
          })
        ).then(() => wrapup(), wrapup);
      });
    }
  });

  /**
   * Correctly call the aggregation framework to return a cursor with batchSize 1 and get the first result using next
   *
   * @ignore
   */
  it(
    'should ensure MaxTimeMS is correctly passed down into command execution when using a cursor',
    {
      // Add a tag that our runner can trigger on
      // in this case we are setting that node needs to be higher than 0.10.X to run
      metadata: {
        requires: {
          mongodb: '>=2.6.0',
          topology: 'single',
          node: '>0.10.0'
        }
      },

      // The actual test we wish to run
      test: function(done) {
        var client = this.configuration.newClient({ w: 1 }, { poolSize: 1 }),
          databaseName = this.configuration.db;

        // DOC_LINE var db = new Db('test', new Server('localhost', 27017));
        // DOC_START
        client.connect(function(err, client) {
          var db = client.db(databaseName);

          // Some docs for insertion
          var docs = [
            {
              title: 'this is my title',
              author: 'bob',
              posted: new Date(),
              pageViews: 5,
              tags: ['fun', 'good', 'fun'],
              other: { foo: 5 },
              comments: [
                { author: 'joe', text: 'this is cool' },
                { author: 'sam', text: 'this is bad' }
              ]
            }
          ];

          // Create a collection
          var collection = db.collection('shouldCorrectlyDoAggWithCursorMaxTimeMSSet');
          // Insert the docs
          collection.insert(docs, { w: 1 }, function(err, result) {
            expect(result).to.exist;
            expect(err).to.not.exist;

            // Execute aggregate, notice the pipeline is expressed as an Array
            var cursor = collection.aggregate(
              [
                {
                  $project: {
                    author: 1,
                    tags: 1
                  }
                },
                { $unwind: '$tags' },
                {
                  $group: {
                    _id: { tags: '$tags' },
                    authors: { $addToSet: '$author' }
                  }
                }
              ],
              {
                cursor: { batchSize: 1 },
                maxTimeMS: 1000
              }
            );

            // Override the db.command to validate the correct command
            // is executed
            var cmd = db.command;
            // Validate the command
            db.command = function(c) {
              expect(err).to.be.null;
              expect(c.maxTimeMS).to.equal(1000);

              // Apply to existing command
              cmd.apply(db, Array.prototype.slice.call(arguments, 0));
            };

            // Iterate over all the items in the cursor
            cursor.next(function(err, result) {
              expect(err).to.be.null;
              expect(result._id.tags).to.equal('good');
              expect(result.authors).to.eql(['bob']);

              // Validate the command
              db.command = function(c) {
                expect(err).to.be.null;
                expect(c.maxTimeMS).to.equal(1000);

                // Apply to existing command
                cmd.apply(db, Array.prototype.slice.call(arguments, 0));
              };

              // Execute aggregate, notice the pipeline is expressed as an Array
              collection.aggregate(
                [
                  {
                    $project: {
                      author: 1,
                      tags: 1
                    }
                  },
                  { $unwind: '$tags' },
                  {
                    $group: {
                      _id: { tags: '$tags' },
                      authors: { $addToSet: '$author' }
                    }
                  }
                ],
                {
                  maxTimeMS: 1000
                },
                function(err, r) {
                  expect(err).to.not.exist;
                  expect(r).to.exist;

                  // Return the command
                  db.command = cmd;
                  client.close();
                  done();
                }
              );
            });
          });
        });
        // DOC_END
      }
    }
  );

  it('should pass a comment down via the aggregation command', {
    metadata: {
      requires: {
        mongodb: '>=3.5.0',
        topology: 'single',
        node: '>=4.8.5'
      }
    },
    test: function(done) {
      const client = this.configuration.newClient({ w: 1 }, { poolSize: 1 });
      const databaseName = this.configuration.db;

      const comment = 'Darmok and Jalad at Tanagra';

      client.connect(function(err, client) {
        expect(err).to.be.null;

        const db = client.db(databaseName);
        const collection = db.collection('testingPassingDownTheAggregationCommand');

        const command = db.command;

        db.command = function(c) {
          expect(c).to.be.an('object');
          expect(c.comment)
            .to.be.a('string')
            .and.to.equal('comment');
          command.apply(db, Array.prototype.slice.call(arguments, 0));
        };

        collection.aggregate([{ $project: { _id: 1 } }], { comment }, function(err, r) {
          expect(err).to.be.null;
          expect(r).to.not.be.null;
          done();
        });
      });
    }
  });

  /**
   * Correctly call the aggregation framework to return a cursor with batchSize 1 and get the first result using next
   *
   * @ignore
   */
  it('should correctly handle ISODate date matches in aggregation framework', {
    // Add a tag that our runner can trigger on
    // in this case we are setting that node needs to be higher than 0.10.X to run
    metadata: {
      requires: {
        mongodb: '>=2.6.0',
        topology: 'single',
        node: '>0.10.0'
      }
    },

    // The actual test we wish to run
    test: function(done) {
      var databaseName = this.configuration.db;
      var client = this.configuration.newClient(this.configuration.writeConcernMax(), {
        poolSize: 1
      });

      // DOC_LINE var client = new MongoClient(new Server('localhost', 27017));
      // DOC_START
      client.connect(function(err, client) {
        expect(err).to.be.null;

        var db = client.db(databaseName);
        var date1 = new Date();
        date1.setHours(date1.getHours() - 1);

        // Some docs for insertion
        var docs = [
          {
            a: date1,
            b: 1
          },
          {
            a: new Date(),
            b: 2
          }
        ];

        // Create a collection
        var collection = db.collection('shouldCorrectlyQueryUsingISODate');
        // Insert the docs
        collection.insertMany(docs, { w: 1 }, function(err, result) {
          expect(result).to.exist;
          expect(err).to.be.null;

          // Execute aggregate, notice the pipeline is expressed as an Array
          var cursor = collection.aggregate([
            {
              $match: {
                a: new Date(date1.toISOString())
              }
            }
          ]);

          // Iterate over all the items in the cursor
          cursor.next(function(err, result) {
            expect(err).to.be.null;
            expect(result.b).to.equal(1);

            client.close();
            done();
          });
        });
      });
      // DOC_END
    }
  });

  /**
   * Correctly call the aggregation framework to return a cursor with batchSize 1 and get the first result using next
   *
   * @ignore
   */
  it('should correctly exercise hasNext function on aggregation cursor', {
    metadata: {
      requires: {
        mongodb: '>=2.6.0',
        topology: 'single',
        node: '>0.10.0'
      }
    },

    // The actual test we wish to run
    test: function(done) {
      var databaseName = this.configuration.db;
      var client = this.configuration.newClient(this.configuration.writeConcernMax(), {
        poolSize: 1
      });

      // DOC_LINE var client = new MongoClient(new Server('localhost', 27017));
      // DOC_START
      client.connect(function(err, client) {
        expect(err).to.be.null;

        var db = client.db(databaseName);
        // Create a collection
        var collection = db.collection('shouldCorrectlyQueryUsingISODate3');
        // Insert the docs
        collection.insertMany([{ a: 1 }, { b: 1 }], { w: 1 }, function(err, result) {
          expect(result).to.exist;
          expect(err).to.be.null;

          // Execute aggregate, notice the pipeline is expressed as an Array
          var cursor = collection.aggregate([
            {
              $match: {}
            }
          ]);

          // Iterate over all the items in the cursor
          cursor.hasNext(function(err, result) {
            expect(err).to.be.null;
            expect(result).to.equal(true);

            client.close();
            done();
          });
        });
      });
      // DOC_END
    }
  });
});

I think we should endeavor to clean up non-exhausted cursors when the parent client is closed - I don't think this should be our policy, or something we're educating our users to do explicitly, it's too error prone in the real world