I think what you may probably need is to run your tests programmatically.

Read this thread,
ExUnit tests from a module instead of command line/mix

and the implementation of the test task in Mix. (look for the run/1 function)
elixir/test.ex at master · elixir-lang/elixir · GitHub

More on the subject,
If you are hacking Mix.Tasks.Test
read this article by @dnlserrano
dnlserrano.github.io/2019-05-26-exunit-deep-dive.markdown at master · dnlserrano/dnlserrano.github.io · GitHub

Also a recent library from @devonestes seem to do something similar.
muzak/runner.ex at 63166c0a2526cda60787c22127be8645cc13e4dd · devonestes/muzak · GitHub

I haven’t tested it, but this is this looks like the minimum code required in this test in this library.
nimler/test_all.exs at master · wltsmrz/nimler · GitHub

How did I find out all this?
https://github.com/search?q="require_and_run"&type=code

You don’t need to do that. You can do this in your mix.exs:

  def project do
    [
      app: :your_app,
      version: "1.2.3",
      elixir: "~> 1.14.0",
      elixirc_paths: elixirc_paths(Mix.env()),     # 👈 NOTICE THIS
      compilers: [:phoenix] ++ Mix.compilers(),
      start_permanent: Mix.env() == :prod,
      aliases: aliases(),
      deps: deps()
    ]
  end

  defp elixirc_paths(:test), do: ["lib", "test/support"]
  defp elixirc_paths(_), do: ["lib"]

And then put everything that you want to have access to in tests in test/support. I don’t think you should put it in the root test/ directory however.

When I run a set of tests especially when I run it virtual machine I need a way to run a set of tests at one time and run some of them again in case of failure.

If you want to retry failed tests a few times, instead of running mix test, you can run mix test || mix test --failed || mix test --failed

Another thing, because I’m using VM to run the tests I need a way to send messages to Slack so I can easily monitor the results.

Your CI provider can probably handle this for you. If you have rolled this by hand, you’ll need to build that yourself.

What I’m looking for is a way to run the all tests in one run in the order that I want and to get access to the action before the tests started between them and before they finished.

Not really sure what you’re asking here, but there are ExUnit callbacks you can hook into for different parts of the test lifecycle: ExUnit.Callbacks — ExUnit v1.11.3

I believe if you use test --seed 0 your tests will run in the same order each time. Perhaps that will help? From mix help test:

*  --seed - seeds the random number generator used to randomize the order
    of tests; --seed 0 disables randomization