test: add unit tests for selectServers method

Author: mbroadst

test/unit/sdam/server_selection/select_servers_tests.js

@@ -0,0 +1,74 @@
+'use strict';
+const ReadPreference = require('../../../../lib/core/topologies/read_preference');
+const Topology = require('../../../../lib/core/sdam/topology');
+const Server = require('../../../../lib/core/sdam/server');
+const serverSelection = require('../../../../lib/core/sdam/server_selection');
+const selectServers = serverSelection.selectServers;
+const sc = require('../../../../lib/core/sdam/common');
+const expect = require('chai').expect;
+const sinon = require('sinon');
+
+describe('selectServers', function() {
+  beforeEach(function() {
+    this.sinon = sinon.sandbox.create();
+  });
+
+  afterEach(function() {
+    this.sinon.restore();
+  });
+
+  it('should error immediately if timeout exceeds start time', function(done) {
+    const topology = new Topology('invalid:27019');
+    const start = process.hrtime();
+    start[0] = start[0] - 500;
+
+    selectServers(topology, ReadPreference.primary, 500, start, err => {
+      expect(err).to.exist;
+      done();
+    });
+  });
+
+  it('should timeout if no servers are found within `serverSelectionTimeoutMS`', function(done) {
+    const topology = new Topology('someserver:27019');
+    topology.s.state = sc.STATE_CONNECTED; // fake that we are already connected
+
+    selectServers(topology, ReadPreference.primary, 500, process.hrtime(), err => {
+      expect(err).to.exist;
+      expect(err).to.match(/Server selection timed out/);
+      expect(err).to.not.have.property('reason');
+
+      done();
+    });
+  });
+
+  it('should schedule monitoring if no suitable server is found', function(done) {
+    const topology = new Topology('someserver:27019');
+    const serverMonitor = this.sinon.stub(Server.prototype, 'monitor');
+
+    this.sinon
+      .stub(Topology.prototype, 'selectServer')
+      .callsFake(function(selector, options, callback) {
+        const server = Array.from(this.s.servers.values())[0];
+        callback(null, server);
+      });
+
+    this.sinon.stub(Server.prototype, 'connect').callsFake(function() {
+      this.emit('connect');
+    });
+
+    topology.connect(() => {
+      selectServers(topology, ReadPreference.primary, 1000, process.hrtime(), err => {
+        expect(err).to.exist;
+        expect(err).to.match(/Server selection timed out/);
+        expect(err).to.not.have.property('reason');
+
+        // expect a call to monitor for initial server creation, and another for the server selection
+        expect(serverMonitor)
+          .property('callCount')
+          .to.equal(2);
+
+        topology.close(done);
+      });
+    });
+  });
+});