It seems you got something wrong, take a look at: GitHub - KronicDeth/intellij-elixir: Elixir plugin for JetBrain's IntelliJ Platform (including Rubymine). This plugin is way before elixir-ls was a thing and it has amazing support, and a better set of features compared to all other plugins on the market.
But right now tried to set a breakpoint into the code and run tests with debugger - it does not even start running tests, but waits forever until debugger attaches. Some time ago I was able to set a breakpoint, but not evaluate anything when breakpoint was reached - it just crashed Elixir/Erlang process.
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