Bug: Testing in IL2CPP throws strange error on startup

[applejag]

Expected behavior

When running playmode tests in standalone with Unity Test Framework when targeting Windows using IL2CPP as scripting backend that the built client starts and begins running tests without any user interaction.

Actual behavior

When built testing player starts a popup is shown with an error.

• Clicking "Ignore" actually just ignores the error and the tests starts running.
• Clicking "Retry" results in an error that stops the execution.

I've experienced this error for a long while now. Have not spent the time to backtrack when it appeared. At least since september 2019 I think, when the package still was at 12.0.101

This error does not appear on any other IL2CPP builds, only when building Newtonsoft.Json-for-Unity.Tests

Steps to reproduce

• Open the Newtonsoft.Json-for-Unity.Tests project within the repo
• In "Project Settings", change the "Scripting Backend" to "IL2CPP"
• Open the Test Runner window
• With "PlayMode" tab selected, click "Run all in player (StandaloneWindows)"
• Watch it compile
• Once started, see the error message pop up

Details

Host machine OS running Unity Editor 👉 Windows 10 Pro 10.0.18363

Unity build target 👉 Windows standalone, with IL2CPP as scripting backend

Newtonsoft.Json-for-Unity package version 👉 12.0.301

I was using Unity version 👉 2018.4.14f1, 2019.2.11f1

Checklist

• Shutdown Unity, deleted the /Library folder, opened project again in Unity, and problem still remains.
• Checked to be using latest version of the package.