title: Can't create instance variable using before_suite method in miniTest
body: <p>I want create a <code>@conn</code> before all test case and can be used for all test case so i did something like:</p>
  
  <pre><code>class SQLTest &lt; Test::Unit::TestCase
      def self.before_suite                                                       
          @conn = PG.connect(dbname:'MapSwitcher',host:'localhost', user:'Lin')
      end
      def  test_employee_table_have_5_entries
          result = @conn.exec("SELECT COUNT(*) FROM employees")
          assert_equal(result.getvalue(0,0).to_i, 5)
       end
  
  end
  </code></pre>
  
  <p>And I got an error:</p>
  
  <pre><code>noMethodError: private method `exec' called for nil:NilClass
  </code></pre>
  
  <p>it seems like the <code>@conn</code> can't be accessed in the test case, </p>