Running/debugging tests in VSCode with ElixirLS

I’m trying to set up a nice debugging experience in my pretty bog-standard Phoenix app using VSCode and ElixirLS. Currently it kind of works but there are a number of issues with it:

  • The tests run very slowly compared to mix test (221s vs 7s)
  • The debugger output is very noisy and interspersed with errors that don’t arise during a normal test run.
  • The debugger hangs at the end of the test run and has to be manually stopped

I’m using the default config as generated by ElixirLS:

{
  "version": "0.2.0",
  "configurations": [
    {
      "type": "mix_task",
      "name": "mix test",
      "request": "launch",
      "task": "test",
      "taskArgs": [
        "--trace"
      ],
      "startApps": true,
      "projectDir": "${workspaceRoot}",
      "requireFiles": [
        "test/**/test_helper.exs",
        "test/**/*_test.exs"
      ]
    }
  ]
}

Here’s the output from starting the debugger:

Started ElixirLS debugger v0.5.0
Elixir version: "1.10.3 (compiled with Erlang/OTP 22)"
Erlang version: "23"
ElixirLS compiled with Elixir 1.7.4 and erlang 20
# lots of Bcrypt errors 🤷‍♂️

I’d also like to be able to only run tests for the current file, or even just the current test. I believe vscode exposes various interpolations for launch configs.

Has anyone managed to get a nice test debugging experience in vscode with Elixir? Are there any changes I can make to fix the above problems.?

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Using Visual Studio Code to debug Jest based unit tests, please follow the below steps.

Setting up configuration

Step 1: Enable debugging in our project.
Step 2: Configuring the ElixirJS test debugging single run.
Step 3: Debugging our project.

Your configuration seems right and I don’t know what version you are using of VSCode but right now the test experience in VSCode with Elixir is good.

Best Regards,

I’m not sure you understood my question. It has nothing to do with Jest or JavaScript. These are Elixir tests that use ExUnit. The steps you mention don’t explain anything either.

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It is expected to be significantly slower since in debugging mode all of the modules in the application need to be instrumented to accept breakpoints.

it’s not too surprising that some test would fail since the previously mentioned debugging delay could cause some GenServer.call's to fail due to timeouts. Although I generally wouldn’t expect too many issues from this.

This is expected

I’m not sure of a nice way of doing this but you might be able to manually edit the "task": "test", line to have the line number of the test to run. Something like: "task": "test test/providers/workspace_symbols_test.exs:37",. But as you mention some sort of interpolation should be possible, maybe you can find some ideas this VSCode testing extention: https://marketplace.visualstudio.com/items?itemName=samuel-pordeus.elixir-test

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I’m running into a similar problem. Would love to understand how others are using elixirls and vscode debugger.

Same here. I want to debug the app whilst running a test.

Could anyone share their configuration or at least describe the best possible debugging experience to date? Which IDE, plugins, etc?

Being new to the ecosystem and being used to a super smooth debugging experience (JVM) I’m feeling overwhelmed and underwhelmed at the same time :slight_smile:

Could you say a bit more as to why please? Is there a way to modify this behaviour?

Here’s an example that works, although the by line test is a bit less convenient since your cursor must be on the precise line of the test you want to run:

{
  "version": "0.2.0",
  "configurations": [
    {
      "type": "mix_task",
      "name": "mix test",
      "request": "launch",
      "task": "test",
      "taskArgs": [],
      "startApps": true,
      "projectDir": "${workspaceRoot}",
      "requireFiles": ["test/**/test_helper.exs", "test/**/*_test.exs"]
    },
    {
      "type": "mix_task",
      "name": "mix test current file",
      "request": "launch",
      "task": "test",
      "taskArgs": [
        "${relativeFile}"
      ],
      "startApps": true,
      "projectDir": "${workspaceRoot}",
      "requireFiles": [
        "test/**/test_helper.exs",
        "${relativeFile}"
      ]
    },
    {
      "type": "mix_task",
      "name": "mix test current line number",
      "request": "launch",
      "task": "test",
      "taskArgs": [
        "${relativeFile}:${lineNumber}"
      ],
      "startApps": true,
      "projectDir": "${workspaceRoot}",
      "requireFiles": [
        "test/**/test_helper.exs",
        "${relativeFile}"
      ]
    }
  ]
}

Any thoughts on how we might be able to speed this up? Some performance degradation is fine (and I imagine unavoidable) but it’s incredibly slow to use at the moment, and often quicker to add a few IO.inspect statements. Perhaps there is a way of specifying only certain modules that we’re interested in instrumenting?

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