stringify-error: improve stringify unit tests

Add tests to check if strinfigy can handle error object

test/unit/utils.js

@@ -4,7 +4,7 @@ const winston = require('winston')
 const { test } = require('ava')
 const utils = require('../../src/utils')
 
-test('parseStringToJSON: with a valid JSON string', t => ( 
+test('parseStringToJSON: with a valid JSON string', t => (
   utils.parseStringToJSON(JSON.stringify({ name: 'Papyrus' }))
     .then(result => t.deepEqual(result, { name: 'Papyrus' }))
 ))
@@ -22,6 +22,14 @@ test('stringify: with a invalid JSON object', t => {
   t.is(utils.stringify('Papyrus'), 'Papyrus')
 })
 
+test('stringify: with a valid error object', t => {
+  const error = new Error('Error Message')
+  const { message, stack } = JSON.parse(utils.stringify(error))
+
+  t.is(message, 'Error Message')
+  t.true(stack.includes('Error: Error Message'))
+})
+
 test('generateLogLevel: with status code 400', t => {
   t.is(utils.generateLogLevel(400), 'warn')
 })