Let minitest parse ARGV:

- ### Problem

  See rails#54647 for the original reason this needs to be fixed.

  ### Context

  rails#54647 was reverted as we thought it broke running
  `bin/rails test test:system` where in fact this command was never
  a valid command, but it was previously silently ignoring the
  `test:system` arg (anything not considered a path is discarded).

  rails#54647 was in some way a better behaviour as it was at least
  failing loudly.

  Whether `bin/rails test test:system` should be supported
  (as discussed [here](rails#54736 (comment))),
  is a different problem that is out of scope of this patch.

  Ultimately, rails#54647 implementation was not broken but the solution
  wasn't elegant and didn't reach any consensus, so I figured let's
  try a new approach.

  ### Solution

  Basically the issue is that it's impossible for the Rails test
  command to know which arguments should be parsed and which should
  be proxied to minitest. And what it tries to achieve is providing
  some sort of CLI that minitest lacks.

  This implementation relies on letting minitest parse all options
  **and then** we load the files. Previously it was the opposite,
  where the rails runner would try to guess what files needs to be
  required, and then let minitest parse all options.
  This is done using a "catch-all non-flag arguments" to minitest
  option parser.

  --------------------

  Now that we delegate the parsing of ARGV to minitest, I had to
  workaround two issues:

  1) Running any test subcommand such as `bin/rails test:system`
     is the equivalent of `bin/rails test test/system`, but in
     the former, ARGV is empty and the "test/system" string is
     passed as a ruby parameter to the main test command.

     So we need to mutate ARGV. *But* mutating argv can only be done
     inside a `at_exit` hook, because any mutation would be rolled
     back when the command exists. This happens before minitest
     has run any test (at process exit).
     https://github.com/rails/rails/blob/f575fca24a72cf0631c59ed797c575392fbbc527/railties/lib/rails/command.rb#L140-L146

  2) Running a test **without** the rails command: `ruby test/my_test.rb`
     would end up loading the `my_test.rb` file twice. First, because
     of `ruby`, and the because of our minitest plugin.
     So we need to let our plugin know whether loading file is required
     (e.g. did the user used the CLI).

Author: Edouard-chin

railties/lib/minitest/rails_plugin.rb

@@ -127,6 +127,11 @@ def self.plugin_rails_options(opts, options)
       options[:profile] = count
     end
 
+    opts.on(/^[^-]/) do |test_file|
+      options[:test_files] ||= []
+      options[:test_files] << test_file
+    end
+
     options[:color] = true
     options[:output_inline] = true
   end
@@ -137,6 +142,10 @@ 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)

railties/lib/rails/test_unit/runner.rb

@@ -26,6 +26,7 @@ class Runner
       TEST_FOLDERS = [:models, :helpers, :channels, :controllers, :mailers, :integration, :jobs, :mailboxes]
       PATH_ARGUMENT_PATTERN = %r"^(?!/.+/$)[.\w]*[/\\]"
       mattr_reader :filters, default: []
+      mattr_reader :load_test_files, default: false
 
       class << self
         def attach_before_load_options(opts)
@@ -52,10 +53,14 @@ def run_from_rake(test_command, argv = [])
           success || exit(false)
         end
 
-        def run(argv = [])
-          load_tests(argv)
-
+        def run(args = [])
           require "active_support/testing/autorun"
+
+          @@load_test_files = true
+
+          at_exit do
+            ARGV.replace(args)
+          end
         end
 
         def load_tests(argv)
@@ -93,8 +98,6 @@ def compose_filter(runnable, filter)
           def extract_filters(argv)
             # Extract absolute and relative paths but skip -n /.*/ regexp filters.
             argv.filter_map do |path|
-              next unless path_argument?(path)
-
               path = path.tr("\\", "/")
               case
               when /(:\d+(-\d+)?)+$/.match?(path)

railties/test/application/test_runner_test.rb

@@ -222,6 +222,69 @@ def test_sanae
       end
     end
 
+    def test_run_test_at_root
+      app_file "my_test.rb", <<-RUBY
+        require "test_helper"
+
+        class MyTest < ActiveSupport::TestCase
+          def test_rikka
+            puts 'Rikka'
+          end
+        end
+      RUBY
+
+      run_test_command("my_test.rb").tap do |output|
+        assert_match "Rikka", output
+      end
+    end
+
+    def test_run_test_having_a_slash_in_its_name
+      app_file "my_test.rb", <<-RUBY
+        require "test_helper"
+
+        class MyTest < ActiveSupport::TestCase
+          test "foo/foo" do
+            puts 'Rikka'
+          end
+        end
+      RUBY
+
+      run_test_command("my_test.rb -n foo\/foo").tap do |output|
+        assert_match "Rikka", output
+      end
+    end
+
+    def test_run_test_with_flags_unordered
+      app_file "my_test.rb", <<-RUBY
+        require "test_helper"
+
+        class MyTest < ActiveSupport::TestCase
+          test "foo/foo" do
+            puts 'Rikka'
+          end
+        end
+      RUBY
+
+      run_test_command("--seed 344 my_test.rb --fail-fast -n foo\/foo").tap do |output|
+        assert_match "Rikka", output
+      end
+    end
+
+    def test_run_test_after_a_flag_without_argument
+      app_file "my_test.rb", <<-RUBY
+        require "test_helper"
+        class MyTest < ActiveSupport::TestCase
+          test "foo/foo" do
+            puts 'Rikka'
+          end
+        end
+      RUBY
+
+      run_test_command("--fail-fast my_test.rb -n foo\/foo").tap do |output|
+        assert_match "Rikka", output
+      end
+    end
+
     def test_run_matched_test
       app_file "test/unit/chu_2_koi_test.rb", <<-RUBY
         require "test_helper"