Active Record bin/test command runs only its own adapter tests

There are two ways to run unit tests. `bundle exec rake test` and
`bin/test`. Active Record `bundle exec rake test` only executes its
own adapter specific tests. on the other hand, `bin/test` executes all
adapter specfic tests then some test files need to have `if
current_adapter?`, which can be removed.

- Removed `require_relative "../../tools/test"` to require its own one
- `default_test_exclude_glob` excludes all of adapter specific tests.
- `list_tests(argv)` adds its own adapter specific tests
- `adapter_short` method extracted to get the short hand adapter name
  like `sqlite3`, `mysql2` and `postgresql` via `ENV["ARCONN"]`

activerecord/bin/test

@@ -8,7 +8,7 @@ if adapter_index
 end
 
 COMPONENT_ROOT = File.expand_path("..", __dir__)
-require_relative "../../tools/test"
+require_relative "../test/support/tools"
 
 module Minitest
   def self.plugin_active_record_options(opts, options)

activerecord/test/support/tools.rb

@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+$: << File.expand_path("test", COMPONENT_ROOT)
+
+require "bundler/setup"
+
+require "rails/test_unit/runner"
+require "rails/test_unit/reporter"
+require "rails/test_unit/line_filtering"
+require "active_support"
+require "active_support/test_case"
+
+require "rake/testtask"
+Rails::TestUnit::Runner.singleton_class.prepend Module.new {
+   private
+     def list_tests(argv)
+       tests = super
+       tests.concat FileList["test/cases/adapters/#{adapter_short}/**/*_test.rb"]
+     end
+
+     def default_test_exclude_glob
+       ENV["DEFAULT_TEST_EXCLUDE"] || "test/cases/adapters/*/*_test.rb"
+     end
+
+     def adapter_short
+       ENV["ARCONN"] || "sqlite3"
+     end
+ }
+
+ActiveSupport::TestCase.extend Rails::LineFiltering
+Rails::TestUnitReporter.app_root = COMPONENT_ROOT
+Rails::TestUnitReporter.executable = "bin/test"
+
+Rails::TestUnit::Runner.parse_options(ARGV)
+Rails::TestUnit::Runner.run(ARGV)