If you’re using the vscode-elixir extension then the author gives you a task runner snippet to build and test. You will need to create your project using mix, which I didn’t know at the time.
Details; vscode-elixir/README.md at master · timmhirsens/vscode-elixir · GitHub
You might want to look at this PR for the elixir plugin. I tried the run highlighted code in tonight and it works for basic stuff. But it does not have the context of your project, so you can’t running anything specific to your project (at least that’s my impression.
I started playing around with the editor tonight. I currently use Sublime Test. So far, I’m impressed with VS Code.
I’ve just released a VS Code extension that includes debugger integration: https://medium.com/@JakeBeckerCode/introducing-elixirls-the-elixir-language-server-d449bbbdfc01
It’s pretty rough right now, but basic step debugging with line breakpoints works. Give it a try!