Basic implementation done, need to UTR changes + sync spec tests still

src/error.ts

@@ -200,6 +200,7 @@ export class MongoError extends Error {
  * @category Error
  */
 export class MongoServerError extends MongoError {
+  errorResponse?: ErrorDescription;
   codeName?: string;
   writeConcernError?: Document;
   errInfo?: Document;
@@ -223,9 +224,17 @@ export class MongoServerError extends MongoError {
       this[kErrorLabels] = new Set(message.errorLabels);
     }
 
+    this.errorResponse = message;
+
     for (const name in message) {
-      if (name !== 'errorLabels' && name !== 'errmsg' && name !== 'message')
+      if (
+        name !== 'errorLabels' &&
+        name !== 'errmsg' &&
+        name !== 'message' &&
+        name !== 'errorResponse'
+      ) {
         this[name] = message[name];
+      }
     }
   }
 

test/unit/error.test.ts

@@ -113,6 +113,24 @@ describe('MongoErrors', () => {
       expect(err.message).to.equal(errorMessage);
       expect(err.someData).to.equal(12345);
     });
+    context('errorResponse property', function () {
+      it(`should set errorResponse to raw results document passed in`, function () {
+        const errorDoc = { message: 'A test error', someData: 12345 };
+        const err = new MongoServerError(errorDoc);
+        expect(err).to.be.an.instanceof(Error);
+        expect(err.errorResponse).to.deep.equal(errorDoc);
+      });
+      it(`should not construct enumerated key 'errorResponse' if present`, function () {
+        const errorDoc = {
+          message: 'A test error',
+          errorResponse: 'I will not be an enumerated key'
+        };
+        const err = new MongoServerError(errorDoc);
+        expect(err).to.be.an.instanceof(Error);
+        expect(err.errorResponse).to.deep.equal(errorDoc);
+        expect(err.errorResponse?.errorResponse).to.deep.equal('I will not be an enumerated key');
+      });
+    });
   });
 
   describe('MongoNetworkError#constructor', () => {