```ruby
# -*- coding: utf-8 -*-
#
# Copyright (C) 2012  Kouhei Sutou <kou@clear-code.com>
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

require "test-unit"
require "test/unit/assertion-failed-error"
require 'active_support/testing/assertions'

module ActiveSupport
  if const_defined?(:TestCase)
    remove_const :TestCase
  end

  class TestCase < ::Test::Unit::TestCase
    include ActiveSupport::Testing::Assertions

    Assertion = ::Test::Unit::AssertionFailedError
  end
end
```

Use double quote (") for string literal
user
```ruby
# -*- coding: utf-8 -*-
#
# Copyright (C) 2012  Kouhei Sutou <kou@clear-code.com>
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

require "test-unit"
require "test/unit/assertion-failed-error"
require "active_support/testing/assertions"

module ActiveSupport
  if const_defined?(:TestCase)
    remove_const :TestCase
  end

  class TestCase < ::Test::Unit::TestCase
    include ActiveSupport::Testing::Assertions

    Assertion = ::Test::Unit::AssertionFailedError
  end
end
```
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