Getting all files containing a failed test from a jest run

The past 2 days has seen 2 of us at ahead upgrading from react router 5 to version 6 (or remix router v1 as I like to call it, because it is considerably different to version 5).

Once we did all possible preparations while still being on V5, we could either

• use a package that helps in a migration
• pull the plug, upgrade the dependencies and let Typescript guide us in the process of fixing the app

Of course we underestimated the effort somewhat, even so after 2 days we can conclude that the upgrade was successful. At one point, however, we were looking at 85 failing tests across numerous test files. If you know jest, and have searched around a bit you will find that it is not even that simple to get a simple straightforward list of file names in which failing tests reside.

The following approach is one way to get a list of file names with failed tests after all.

You can run jest such that it will output a json file containing all outcomes of the tests:

jest --json --outputFile=testrun.json

A typical output looks like that:

{
  "numFailedTestSuites": 0,
  "": "...",
  "snapshot": {
    "added": 0,
    "": "...",
  },
  "testResults": [
    {
      "assertionResults": [
        {
          "ancestorTitles": ["features/stories/StoryRoutes"],
          "": "...",
          "title": "unmounts story on onmount"
        },
      ],
      "name": "/.../StoryRoutes.spec.tsx",
      "": "...",
    },

Once you have the test, you can download/install the json query tool jq which will help extract the information that is relevant for us. Since I am on OSX I did

brew install jq

jq has many ways to extract, aggregate and even manipulate json from the command line with a fairly elaborate syntax. With that in mind, we can use a query to obtain the relevant info:

cat testrun.json | jq '[.testResults[] | select(.status == "failed") | .name | split("/") | .[-1:]] | flatten'

The above query will

• find all elements inside the testResults array whose status property matches failed
• take the name property, split it on slashes (the output may vary according to your OS), and take the last element of the resulting array
• the above is packed into one big array which is subsequently flattened.

That way you get a simple list that contains the file names of all test files that contain at least one failed test.