fix(collection): ensure findAndModify always use readPreference primary

Fixes NODE-1541

lib/operations/collection_ops.js

@@ -491,6 +491,8 @@ function findAndModify(coll, query, sort, doc, options, callback) {
     queryObject.bypassDocumentValidation = finalOptions.bypassDocumentValidation;
   }
 
+  finalOptions.readPreference = ReadPreference.primary;
+
   // Have we specified collation
   decorateWithCollation(queryObject, coll, finalOptions);
 

test/functional/find_and_modify_tests.js

@@ -2,6 +2,7 @@
 var f = require('util').format;
 var test = require('./shared').assert;
 var setupDatabase = require('./shared').setupDatabase;
+const expect = require('chai').expect;
 
 describe('Find and Modify', function() {
   before(function() {
@@ -202,4 +203,31 @@ describe('Find and Modify', function() {
       });
     }
   });
+
+  it('should allow all findAndModify commands with non-primary readPreference', {
+    // 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: { topology: 'replicaset' }
+    },
+
+    // The actual test we wish to run
+    test: function(done) {
+      const configuration = this.configuration;
+      const client = configuration.newClient({ readPreference: 'secondary' }, { poolSize: 1 });
+      client.connect((err, client) => {
+        const db = client.db(configuration.db);
+        expect(err).to.be.null;
+
+        const collection = db.collection('findAndModifyTEST');
+        // Execute findOneAndUpdate
+        collection.findOneAndUpdate({}, { $set: { a: 1 } }, err => {
+          expect(err).to.be.null;
+
+          client.close();
+          done();
+        });
+      });
+    }
+  });
 });