This is related to the issue I raised here:
TLDR version of this: NUnit fails to run tests that use Moq or Castle Proxies - its a known bug in Mono.
Also related to the Slack discussion with @viktorbenei in #general.
To fix my issue the Mono version needs to be upgraded. I’ve done some testing and it appears the Mono version currently being used by the Xamarin beta stack fixes the issue.
Mono 5.4.0.0201 has the issue. This is the version that Vs4Mac from the stable channel installs.
It appears to be fixed in 126.96.36.199.
Is it possible to create a step/script to install a specific version of Mono?