The eclipse ide has a nice little feature which will create a unit test for a java file.

I was hoping you could add something similar.

I have a file in:

lib/src/docker/images.dart

I open the vscode explorer to the above file and open the context menu for that file.
There is an option 'create unit test'

The option creates a library as per:
test/src/docker/images_test.dart

A nice bonus is that it generates a basic template for a unit test.