diff --git a/tools/src/tester/ChapterEvaluator.ts b/tools/src/tester/ChapterEvaluator.ts
index db0f8bafd..1cb4a1723 100644
--- a/tools/src/tester/ChapterEvaluator.ts
+++ b/tools/src/tester/ChapterEvaluator.ts
@@ -86,15 +86,14 @@ export default class ChapterEvaluator {
   #evaluate_payload_body(response: ActualResponse, expected_payload?: Payload): Evaluation {
     if (expected_payload == null) return { result: Result.PASSED }
     const delta = atomizeChangeset(diff(expected_payload, response.payload))
-    var messages: string[] = []
-    delta.forEach((value, _index, _array) => {
+    var messages: string[] = _.compact(delta.map((value, _index, _array) => {
       switch(value.type) {
         case Operation.UPDATE:
-          return messages.push(`expected ${value.path.replace('$.', '')}='${value.oldValue}', got '${value.value}'`)
+          return `expected ${value.path.replace('$.', '')}='${value.oldValue}', got '${value.value}'`
         case Operation.REMOVE:
-          return messages.push(`missing ${value.path.replace('$.', '')}='${value.value}'`)
+          return `missing ${value.path.replace('$.', '')}='${value.value}'`
       }
-    })
+    }))
     return messages.length > 0 ? { result: Result.FAILED, message: _.join(messages, ', ')} : { result: Result.PASSED }
   }