Strange tests titles on Node.js v12

[litichevskiydv]

🐛 Bug Report

test.each doesn't use test case toString for tests titles generation on Node.js v12 and produces titles like this:

{ toString: [Function: toString] }

To Reproduce

Situation can be reproduced via executing such test on Node.js v12.

describe("Should not use toString", () => {
  const testCases = [
    {
      toString: () => "Clear test title"
    }
  ];

  test.each(testCases)("%s", testCase => {});
});

Expected behavior

Test title ought to be "Clear test title" as it is on Node.js v8 and v10.

Link to repl or repo (highly encouraged)

Test cases for which strange titles are generated:
https://github.com/litichevskiydv/JsUsefulPrimitives/blob/master/tests/manipulation/manipula.test.js

Build log for Node.js v10:
https://travis-ci.org/litichevskiydv/JsUsefulPrimitives/jobs/529938904
Build log for Node.js v12:
https://travis-ci.org/litichevskiydv/JsUsefulPrimitives/jobs/529938905

Run npx envinfo --preset jest

Paste the results here:

  System:
    OS: Linux 4.15 Ubuntu 16.04.6 LTS (Xenial Xerus)
    CPU: (2) x64 Intel(R) Xeon(R) CPU @ 2.30GHz
  Binaries:
    Node: 12.2.0 - ~/.nvm/versions/node/v12.2.0/bin/node
    Yarn: 1.15.2 - /usr/local/bin/yarn
    npm: 6.9.0 - ~/.nvm/versions/node/v12.2.0/bin/npm
  npmPackages:
    jest: 24.8.0 => 24.8.0 

[mattphillips]

Hmm this is strange, we are using util.format to handle the pretty printing of test titles in printf format.

I'd say this is potentially a bug in Node@12, I've just read over the util.format docs and it doesn't mention anything in regards to objects that override the toString method.

@SimenB @thymikee @jeysal what do you guys think, should this be opened up in the node repo?

[SimenB]

@BridgeAR what do you think, is this a bug? I noticed nothing about it in the release notes for node 12 either

[BridgeAR]

This was an intentional change: nodejs/node#26927

I did not expect this change to cause any issues (passing through objects to the util.format %s formatter is mostly a mistake and result in [object Object]). I personally do not think it's a good idea to rely on the toString behavior and I suggest to change the code to a more "direct" way to write the test cases. I'll nevertheless open a PR to check for the presence of toString and only use util.inspect if it's not present on objects.

[BridgeAR]

I just landed a PR in Node.js that should be included in the next version. It makes sure that %s uses toString functions on objects in case the function is defined by the user.

[SimenB]

Awesome, thanks!

[litichevskiydv]

Guys thanks a lot! I've just rerunned tests and titles looks as they were before. I'm closing the issue.

[github-actions]

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