fix(createCollection): Db.createCollection should pass readConcern to new collection (#2026)

* add tests to verify correct readConcern inheritance

* create new test for createCollection

* modernized test

Author: rosemaryy

lib/db.js

@@ -505,7 +505,9 @@ Db.prototype.createCollection = deprecateOptions(
     if (typeof options === 'function') (callback = options), (options = {});
     options = options || {};
     options.promiseLibrary = options.promiseLibrary || this.s.promiseLibrary;
-
+    options.readConcern = options.readConcern
+      ? new ReadConcern(options.readConcern.level)
+      : this.readConcern;
     const createCollectionOperation = new CreateCollectionOperation(this, name, options);
 
     return executeOperation(this.s.topology, createCollectionOperation, callback);

lib/operations/create_collection.js

@@ -22,6 +22,7 @@ const illegalCommandFields = [
   'raw',
   'readPreference',
   'session',
+  'readConcern',
   'writeConcern'
 ];
 

test/functional/readconcern_tests.js

@@ -10,7 +10,7 @@ describe('ReadConcern', function() {
     return setupDatabase(configuration);
   });
 
-  it('Should set local readConcern on db level', {
+  it('Should set local readConcern on db level when using collection method', {
     metadata: { requires: { topology: 'replicaset', mongodb: '>= 3.2' } },
 
     test: function(done) {
@@ -56,6 +56,31 @@ describe('ReadConcern', function() {
     }
   });
 
+  it('Should set local readConcern on db level when using createCollection method', {
+    metadata: { requires: { topology: 'replicaset', mongodb: '>= 3.2' } },
+
+    test: function(done) {
+      // Get a new instance
+      const configuration = this.configuration;
+      const client = configuration.newClient(
+        { w: 1 },
+        { poolSize: 1, readConcern: { level: 'local' } }
+      );
+      client.connect((err, client) => {
+        expect(err).to.not.exist;
+        const db = client.db(configuration.db);
+        expect(db.s.readConcern).to.deep.equal({ level: 'local' });
+
+        // Get a collection using createCollection
+        db.createCollection('readConcernCollection', (err, collection) => {
+          // Validate readConcern
+          expect(collection.s.readConcern).to.deep.equal({ level: 'local' });
+          client.close(done);
+        });
+      });
+    }
+  });
+
   it('Should set majority readConcern on db level', {
     metadata: { requires: { topology: 'replicaset', mongodb: '>= 3.2' } },