feat(NODE-4184): do not throw with explain and write conceern

Author: durran

src/operations/aggregate.ts

@@ -85,12 +85,6 @@ export class AggregateOperation extends CommandOperation<CursorResponse> {
       delete this.options.writeConcern;
     }
 
-    if (this.explain && this.writeConcern) {
-      throw new MongoInvalidArgumentError(
-        'Option "explain" cannot be used on an aggregate call with writeConcern'
-      );
-    }
-
     if (options?.cursor != null && typeof options.cursor !== 'object') {
       throw new MongoInvalidArgumentError('Cursor options must be an object');
     }

test/unit/operations/aggregate.test.js

@@ -7,6 +7,23 @@ describe('AggregateOperation', function () {
   const db = 'test';
 
   describe('#constructor', function () {
+    context('when explain is in the options', function () {
+      context('when writeConcern is set', function () {
+        const operation = new AggregateOperation(db, [], {
+          explain: 'verbose',
+          writeConcern: { w: 1 }
+        });
+
+        it('sets explain on the operation', function () {
+          expect(operation.explain.verbosity).to.equal('verbose');
+        });
+
+        it('sets the write concern on the operation', function () {
+          expect(operation.writeConcern.w).to.equal(1);
+        });
+      });
+    });
+
     context('when out is in the options', function () {
       const operation = new AggregateOperation(db, [], { out: 'test', dbName: db });