Suppose I have a legacy rails or node-js or java project.
I will write a separate new project for tests. I will check all the tests pass.
Then I write a new elixir project and just change endpoint of test.
If all tests pass, I can finally switch.

years ago I have already done it before for a client… writing test in node-js and app was in Rails. It was possible because everything was through REST APIs.

Are there any advancements where I can be sitting in an Elixir project and test validations of Rails app? or test a completely another Elixir project?

It might be difficult to explain.
But think of directory structure like this.

• A Backend app (API / GraphQL) build using Rails or Elixir
• A test app built using Elixir
• A frontend end that connects through REST or GraphQL
• A Mobile app.

As of now I am thinking to build a GraphQL app and another project outside will test this GraphQL project without access to internals. Open to suggestions on how to keep test project Independent and outside main project.