Ran the command:

autorest C:\Users\frross\source\repos\azure-rest-api-specs\specification\cosmos-db\resource-manager\readme.md `
    --csharp --version=v2 --reflect-api-versions `
    --csharp-sdks-folder=C:\Users\frross\source\repos\azure-sdk-for-net\sdk `
    --tags=package-2021-03-preview

The preview release has quite a different structure, so I went back to the last release from it (commit 18e1b96) and copied the test files here. The project builds, but the tests have a couple errors to fix.

The Swagger changes needed were checked in, so rerun autorun from the master branch in the main repo instead of against a local checkout so the metadata is correct.

I had hardcoded a \ instead of using Path.PathSeparator.

Instead of Path.Separator, which is making the build fail, just use a /, which is supported on all platforms.