🚀 Feature: Allow passing in a "target object" for the JSON reporter

[JoshuaKGoldberg]

Feature Request Checklist

• I have read and agree to Mocha's Code of Conduct and Contributing Guidelines
• I have searched for related issues and issues with the faq label, but none matched my issue.
• I want to provide a PR to resolve this

Overview

Filing an issue for #4822, as described by @ashleyfrieze in #4822. The summary is that in some test setups it's not feasible to have Mocha output to a file.

The use case that drove this is where I'm using mocha as the test framework, running it in a virtual browser, driving the tests from a Java application and need to gather the test results from Mocha. I don't have the ability to send them to a file from this environment, but being able to put them into a variable means I can pull the results out at the end.

In particular, I was running mocha inside a Java test. The sut code in question was the embedded javascript being served by the Java application server as part of its SSR. The project, though a Java project, essentially had some JavaScript in it, and wrapping a mocha test within a JUnit test runner required the mocha tests to be executed, but the test runner to be able to acquire the results at the end.

Suggested Solution

Add to the existing configuration options for the JSON reporter by allowing a target object to be provided to be populated with test results.

Alternatives

We could make a duplicate of the JSON reporter, purely for writing to objects. A workaround is to hack in an alternative of the JSON reporter into the reporters in the runner. However, this is such a small addition to the core, and entirely in keeping with the behaviour of producing a JavaScript model of the test results, that it seems to belong in core.

Additional Info

It's a nice to have feature, and pretty innocuous. I worked around it somehow in my project, but could imagine coming back to this and wanting it in future Java SSR situations, or in situations where some mocha tests are being run by a different test framework as part of a transition plan.

See also previous PR: #2651.

[JoshuaKGoldberg]

Now looking at this from the perspective of a maintainer: I'm of the opinion this isn't worth the maintenance cost to include in core.

Having an object that receives properties doesn't work well with how existing reporter options are set up. Reporters generally have options that can also be specified in config file and/or --reporter-option on the CLI. This new option as implemented in #4822 would only be reasonably useful with programmatic usage, right? (did I misinterpret it?)

Another couple alternatives could be to...

• ...make a temp file on disk - which should be doable for most consumers
  • I do question why that wouldn't be doable, if you're already in an environment that can run tests?
• ...run Mocha in a process with stdout parsed and captured in an object
  • Admittedly, that's a little clunky and has some overhead...

IMO a better path might be to make a community fork of the reporter. If that fork ends up getting a lot of usage then we can consider that evidence to build this feature into core.

cc @mochajs/maintenance-crew for more thoughts?