Load tests prior to when Minitest load plugins:

- Fix rails#54741 (comment)
- ### Problem

  Custom minitest plugins that require tests to be loaded (such as
  minitest-focus) may malfunction. This is due to a behaviour change
  introduced in rails#54741.

  ### Context

  Rails now load the test thanks to a custom plugin, but this creates
  a caveat: Any plugins running prior than ours may need the tests
  to be loaded.

  The order of thing in a normal minitest setup is:

  1) Test files are loaded
  2) Minitest load plugins
  3) Minitest initialize plugins

  Before this patch it was:

  1) Minitest load plugins
  2) Minitest initialize plugins
  3) Our plugin loads the test files.

  The plugins are loaded/initialized by Minitest in a random order.

  ### Solution

  I added a OptionsParser callback which get called at the very end of
  the parsing process and is responsible to load the test files.
  The order of thing is now:

  1) Minitest load plugins
  2) Test files are loaded
  3) Minitest initialize the plugins

Author: Edouard-chin

railties/lib/minitest/rails_plugin.rb

@@ -134,6 +134,12 @@ def self.plugin_rails_options(opts, options)
 
     options[:color] = true
     options[:output_inline] = true
+
+    opts.on do
+      if ::Rails::TestUnit::Runner.load_test_files
+        ::Rails::TestUnit::Runner.load_tests(options.fetch(:test_files, []))
+      end
+    end
   end
 
   # Owes great inspiration to test runner trailblazers like RSpec,
@@ -142,10 +148,6 @@ def self.plugin_rails_init(options)
     # Don't mess with Minitest unless RAILS_ENV is set
     return unless ENV["RAILS_ENV"] || ENV["RAILS_MINITEST_PLUGIN"]
 
-    if ::Rails::TestUnit::Runner.load_test_files
-      ::Rails::TestUnit::Runner.load_tests(options.fetch(:test_files, []))
-    end
-
     unless options[:full_backtrace]
       # Plugin can run without Rails loaded, check before filtering.
       if ::Rails.respond_to?(:backtrace_cleaner)