fix: report writeErrors and writeConcernErrors for bulk ops

Collates the `writeErrors` and `writeConcernErrors` reported by bulk operations
and returns them in the `result` object.

lib/bulk.js

@@ -83,6 +83,17 @@ class Bulk {
     const setResult = (cmd, cmdResult) => {
       const cmdKey = Object.keys(cmd)[0];
       result[this.cmdKeys[cmdKey]] += cmdResult.n;
+      // Collate and report writeErrors and writeConcernErrors to the result object.
+      if (cmdResult.writeErrors) {
+        for (const writeError of cmdResult.writeErrors) {
+          result.writeErrors.push(writeError);
+        }
+      }
+      if (cmdResult.writeConcernErrors) {
+        for (const writeConcernError of cmdResult.writeConcernErrors) {
+          result.writeErrors.push(writeConcernError);
+        }
+      }
     }
 
     return this

test/bulk.js

@@ -167,4 +167,23 @@ describe('bulk', function() {
     expect(json.nRemoveOps).to.equal(1, 'Should result in nRemoveOps field set to 1');
     expect(json.nBatches).to.equal(3, 'Should result in nBatches field set to 3');
   });
-});
+
+  it('should collate and report writeErrors', async () => {
+    await db.b.createIndex(
+      {
+        name: 1,
+      },
+      {
+        unique: true,
+        background: true,
+      }
+    );
+
+    const bulk = db.b.initializeUnorderedBulkOp();
+    bulk.insert({ name: 'Charmander' });
+    bulk.insert({ name: 'Charmander' });
+    const result = await bulk.execute();
+    expect(result.writeErrors.length).to.equal(1);
+    expect(result.writeErrors[0].errmsg).to.match(/duplicate key error/);
+  });
+});