add unit test

Author: W-A-James

test/unit/assorted/server_discovery_and_monitoring.test.ts

@@ -0,0 +1,123 @@
+import { expect } from 'chai';
+import { type TopologyDescription } from 'mongodb-legacy';
+import * as sinon from 'sinon';
+
+import {
+  type MongoClient,
+  ObjectId,
+  Server,
+  ServerDescription,
+  Topology,
+  TOPOLOGY_DESCRIPTION_CHANGED,
+  type TopologyDescriptionChangedEvent
+} from '../../mongodb';
+
+const SDAM_EVENTS = [
+  // Topology events
+  TOPOLOGY_DESCRIPTION_CHANGED
+];
+
+describe('Server Discovery and Monitoring', function () {
+  let serverConnect: sinon.SinonStub;
+  let topologySelectServer: sinon.SinonStub;
+  let client: MongoClient;
+  let events: TopologyDescriptionChangedEvent[] = [];
+
+  function getNewDescription() {
+    const [topologyDescriptionChanged] = events.filter(
+      x => x.name === 'topologyDescriptionChanged'
+    );
+    events = [];
+    return topologyDescriptionChanged.newDescription;
+  }
+
+  before(async function () {
+    serverConnect = sinon.stub(Server.prototype, 'connect').callsFake(function () {
+      this.s.state = 'connected';
+      this.emit('connect');
+    });
+    topologySelectServer = sinon
+      .stub(Topology.prototype, 'selectServer')
+      .callsFake(async function (_selector, _options) {
+        topologySelectServer.restore();
+
+        const fakeServer = { s: { state: 'connected' }, removeListener: () => true };
+        return fakeServer;
+      });
+    const events = [];
+    client.on('topologyDescriptionChanged', event => events.push(event));
+    await client.connect();
+  });
+
+  after(function () {
+    serverConnect.restore();
+  });
+
+  describe('when a newer primary is detected', function () {
+    it('steps down original primary to unknown server description with appropriate error message', async function () {
+      let newDescription: TopologyDescription;
+      // Start with a as primary
+      client.topology.serverUpdateHandler(
+        new ServerDescription('a:27017', {
+          ok: 1,
+          helloOk: true,
+          isWritablePrimary: true,
+          hosts: ['a:27017', 'b:27017'],
+          setName: 'rs',
+          setVersion: 1,
+          electionId: ObjectId.createFromHexString('000000000000000000000001'),
+          minWireVersion: 0,
+          maxWireVersion: 21
+        })
+      );
+
+      newDescription = getNewDescription();
+
+      expect(newDescription.type).to.equal('ReplicaSetWithPrimary');
+
+      // b is elected as primary, a gets marked stale
+      client.topology.serverUpdateHandler(
+        new ServerDescription('b:27017', {
+          ok: 1,
+          helloOk: true,
+          isWritablePrimary: true,
+          hosts: ['a:27017', 'b:27017'],
+          setName: 'rs',
+          setVersion: 2,
+          electionId: ObjectId.createFromHexString('000000000000000000000001'),
+          minWireVersion: 0,
+          maxWireVersion: 21
+        })
+      );
+
+      newDescription = getNewDescription();
+
+      let aOutcome = newDescription.servers.get('a:27017');
+      expect(aOutcome.error).to.match(/primary marked stale due to discovery of newer primary/);
+
+      // a still incorrectly reports as primary
+      client.topology.serverUpdateHandler(
+        new ServerDescription('a:27017', {
+          ok: 1,
+          helloOk: true,
+          isWritablePrimary: true,
+          hosts: ['a:27017', 'b:27017'],
+          setName: 'rs',
+          setVersion: 1,
+          electionId: ObjectId.createFromHexString('000000000000000000000001'),
+          minWireVersion: 0,
+          maxWireVersion: 21
+        })
+      );
+
+      newDescription = getNewDescription();
+
+      aOutcome = newDescription.servers.get('a:27017');
+
+      expect(aOutcome.type).to.equal('Unknown');
+      expect(aOutcome.error).to.match(
+        /primary marked stale due to electionId\/setVersion mismatch: server setVersion: \d+, server electionId: \d{24}, topology setVersion: \d, topology electionId: \d{24}/
+      );
+    });
+  });
+});