Use COMPONENT_ROOT as app_root when present in test unit reporting.

railties/lib/rails/test_unit/reporter.rb

@@ -82,6 +82,8 @@ module Rails
         @app_root ||=
           if defined?(ENGINE_ROOT)
             ENGINE_ROOT
+          elsif defined?(COMPONENT_ROOT)
+            COMPONENT_ROOT
           elsif Rails.respond_to?(:root)
             Rails.root
           end

tools/test.rb

@@ -11,14 +11,6 @@ require "rails/test_unit/line_filtering"
 require "active_support"
 require "active_support/test_case"
 
-class << Rails
-  # Necessary to get rerun-snippets working.
-  def root
-    @root ||= Pathname.new(COMPONENT_ROOT)
-  end
-  alias __root root
-end
-
 ActiveSupport::TestCase.extend Rails::LineFiltering
 Rails::TestUnitReporter.executable = "bin/test"