Silences warnings from mongodb client (#5025)

* Silences warnings from mongodb client

* Update count, delete and finds to recommended implementations

* With new parser, readPref will be null by default

* Update flaky specs wih async/await style

* Adds gridstore adapter spec

* Use GridFSBucketStorage adapter

spec/GridStoreAdapter.spec.js

@@ -0,0 +1,99 @@
+const MongoClient = require('mongodb').MongoClient;
+const GridStore = require('mongodb').GridStore;
+
+const GridStoreAdapter = require('../lib/Adapters/Files/GridStoreAdapter')
+  .GridStoreAdapter;
+const Config = require('../lib/Config');
+const FilesController = require('../lib/Controllers/FilesController').default;
+
+// Small additional tests to improve overall coverage
+describe_only_db('mongo')('GridStoreAdapter', () => {
+  it('should properly instanciate the GridStore when deleting a file', async done => {
+    const databaseURI = 'mongodb://localhost:27017/parse';
+    const config = Config.get(Parse.applicationId);
+    const gridStoreAdapter = new GridStoreAdapter(databaseURI);
+    const db = await gridStoreAdapter._connect();
+    db.dropDatabase();
+    const filesController = new FilesController(
+      gridStoreAdapter,
+      Parse.applicationId,
+      {}
+    );
+
+    // save original unlink before redefinition
+    const originalUnlink = GridStore.prototype.unlink;
+
+    let gridStoreMode;
+
+    // new unlink method that will capture the mode in which GridStore was opened
+    GridStore.prototype.unlink = function() {
+      // restore original unlink during first call
+      GridStore.prototype.unlink = originalUnlink;
+
+      gridStoreMode = this.mode;
+
+      return originalUnlink.call(this);
+    };
+
+    filesController
+      .createFile(config, 'myFilename.txt', 'my file content', 'text/plain')
+      .then(myFile => {
+        return MongoClient.connect(databaseURI)
+          .then(client => {
+            const database = client.db(client.s.options.dbName);
+            // Verify the existance of the fs.files document
+            return database
+              .collection('fs.files')
+              .count()
+              .then(count => {
+                expect(count).toEqual(1);
+                return { database, client };
+              });
+          })
+          .then(({ database, client }) => {
+            // Verify the existance of the fs.files document
+            return database
+              .collection('fs.chunks')
+              .count()
+              .then(count => {
+                expect(count).toEqual(1);
+                return client.close();
+              });
+          })
+          .then(() => {
+            return filesController.deleteFile(config, myFile.name);
+          });
+      })
+      .then(() => {
+        return MongoClient.connect(databaseURI)
+          .then(client => {
+            const database = client.db(client.s.options.dbName);
+            // Verify the existance of the fs.files document
+            return database
+              .collection('fs.files')
+              .count()
+              .then(count => {
+                expect(count).toEqual(0);
+                return { database, client };
+              });
+          })
+          .then(({ database, client }) => {
+            // Verify the existance of the fs.files document
+            return database
+              .collection('fs.chunks')
+              .count()
+              .then(count => {
+                expect(count).toEqual(0);
+                return client.close();
+              });
+          });
+      })
+      .then(() => {
+        // Verify that gridStore was opened in read only mode
+        expect(gridStoreMode).toEqual('r');
+
+        done();
+      })
+      .catch(fail);
+  });
+});