Also having this issue in .net core unit test projects. Whats the whole point of having the environment variables present in the property pages of a .net core unit test project when setting them does absolutely nothing.
The workaround in 1831 is not acceptable as it won't work well for redistributable libraries that you intend to unit test. Since Microsoft is pushing the environment variable way of configuration, it should be a first class citizen in unit test projects as well. Not just ASP .NET Core web application projects.