test: add test for custom toJSON methods attached to errors

Author: KyleRoss

lib/LogMessage.test.js

@@ -104,6 +104,17 @@ describe('Statics', () => {
         expect(result).toHaveProperty('stack', err.stack);
         expect(result).toHaveProperty('test', true);
       });
+
+      test('should skip custom toJSON fn if error already has one', () => {
+        const e = new Error('test');
+        const noop = () => { /* noop */ };
+        Object.defineProperty(e, 'toJSON', {
+          value: noop
+        });
+
+        const error = LogMessage.stubError(e);
+        expect(error.toJSON.toString()).toBe(noop.toString());
+      });
     });
   });
 });