exception message in json formatter

Author: innocentiv

package.json

@@ -132,7 +132,7 @@
     "node": ">=0.10"
   },
   "dependencies": {
-    "assertion-error-formatter": "^2.0.0",
+    "assertion-error-formatter": "^2.0.1",
     "babel-runtime": "^6.11.6",
     "bluebird": "^3.4.1",
     "cli-table": "^0.3.1",

src/formatter/json_formatter.js

@@ -3,6 +3,7 @@ import Formatter from './'
 import Status from '../status'
 import { formatLocation, GherkinDocumentParser, PickleParser } from './helpers'
 import { buildStepArgumentIterator } from '../step_arguments'
+import { format } from 'assertion-error-formatter'
 
 const {
   getStepLineToKeywordMap,
@@ -156,7 +157,7 @@ export default class JsonFormatter extends Formatter {
         data.result.duration = testStep.result.duration
       }
       if (status === Status.FAILED && exception) {
-        data.result.error_message = exception.stack || exception
+        data.result.error_message = format(exception)
       }
     }
     if (_.size(testStep.attachments) > 0) {

yarn.lock

@@ -193,9 +193,9 @@ assert@^1.4.0:
   dependencies:
     util "0.10.3"
 
-assertion-error-formatter@^2.0.0:
-  version "2.0.0"
-  resolved "https://registry.yarnpkg.com/assertion-error-formatter/-/assertion-error-formatter-2.0.0.tgz#17a24289cc8440889b54318e6d1187ebee2d5494"
+assertion-error-formatter@^2.0.1:
+  version "2.0.1"
+  resolved "https://registry.yarnpkg.com/assertion-error-formatter/-/assertion-error-formatter-2.0.1.tgz#6bbdffaec8e2fa9e2b0eb158bfe353132d7c0a9b"
   dependencies:
     diff "^3.0.0"
     pad-right "^0.2.2"