it('should use session readPreference', function(done) {
    const configuration = this.configuration;
    const client = this.configuration.newClient(configuration.writeConcernMax(), {
      useUnifiedTopology: true,
      readPreference: 'primaryPreferred'
    });

    client.connect((err, client) => {
      expect(err).to.not.exist;
      this.defer(() => client.close());
      const session = client.startSession({
        readPreference: 'secondary',
        causalConsistency: true
      });

      const result = ReadPreference.resolve(client, { session: session });
      expect(result.mode).to.equal('secondary');
      done();
    });
  });