test(NODE-6492): add integration tests for transaction write concern behavior

test/integration/transactions/transactions.prose.test.ts

@@ -0,0 +1,75 @@
+import { expect } from 'chai';
+import * as semver from 'semver';
+
+import { type MongoClient, type ObjectId } from '../../mongodb';
+
+const metadata: MongoDBMetadataUI = {
+  requires: {
+    topology: '!single'
+  }
+};
+
+describe('Transactions Spec Prose', function () {
+  let client: MongoClient;
+  const started = [];
+
+  beforeEach(async function () {
+    if (
+      semver.satisfies(this.configuration.version, '<=4.2') &&
+      this.configuration.topologyType === 'Sharded'
+    ) {
+      if (this.currentTest) {
+        this.currentTest.skipReason =
+          'Transactions on sharded clusters are only supported after 4.2';
+        this.skip();
+      }
+    }
+    started.length = 0;
+    client = this.configuration.newClient({}, { monitorCommands: true });
+
+    await client
+      .db()
+      .collection('txn-test')
+      .drop()
+      .catch(() => null);
+    await client.db().createCollection('txn-test');
+
+    client.on('commandStarted', ev => started.push(ev));
+  });
+
+  afterEach(async function () {
+    await client
+      ?.db()
+      .collection('txn-test')
+      .drop()
+      .catch(() => null);
+    await client?.close();
+  });
+
+  describe('Options Inside Transaction', function () {
+    it(
+      '1.0 Write concern not inherited from collection object inside transaction.',
+      metadata,
+      async () => {
+        let _id: ObjectId;
+        const collection = client.db().collection('txn-test', { writeConcern: { w: 0 } });
+
+        await client.withSession(async session => {
+          session.startTransaction();
+          _id = (await collection.insertOne({ n: 1 }, { session })).insertedId;
+          await session.commitTransaction();
+        });
+
+        // keep finding until we get a result, otherwise the test will timeout.
+        expect(await collection.findOne({ _id })).to.have.property('n', 1);
+
+        const insertStarted = started.find(ev => ev.commandName === 'insert');
+        expect(insertStarted).to.not.have.nested.property('command.writeConcern');
+
+        // not in asked by the spec test but good to check, this is where the WC would be if it wasn't ignored.
+        const commitTransactionStarted = started.find(ev => ev.commandName === 'commitTransaction');
+        expect(commitTransactionStarted).to.not.have.nested.property('command.writeConcern');
+      }
+    );
+  });
+});