Remove warnings shown when running tests

* For some reason, ActiveRecord was printing a warning saying that
  "active_record/base" was already being loaded and there was a possible
  circular dependency. We fix this by explicitly requiring
  "active_record/base" before `$VERBOSE` is set to true.
* We were getting warnings when re-defining Kernel.capture,
  Kernel.silence_stream and Kernel.silence_stderr, so undefine them
  first.

spec/support/unit/capture.rb

@@ -2,6 +2,8 @@ module Kernel
   # #capture, #silence_stream, and #silence_stderr are deprecated after Rails
   # 4.2 and will be removed in 5.0, so just override them completely here
 
+  undef_method :capture
+
   def capture(stream)
     stream = stream.to_s
     captured_stream = Tempfile.new(stream)
@@ -18,6 +20,8 @@ module Kernel
     stream_io.reopen(origin_stream)
   end
 
+  undef_method :silence_stream
+
   def silence_stream(stream)
     old_stream = stream.dup
     stream.reopen(RbConfig::CONFIG['host_os'] =~ /mswin|mingw/ ? 'NUL:' : '/dev/null')
@@ -28,6 +32,8 @@ module Kernel
     old_stream.close
   end
 
+  undef_method :silence_stderr
+
   def silence_stderr
     silence_stream(STDERR) { yield }
   end

spec/unit_spec_helper.rb

@@ -10,6 +10,8 @@ $test_app = UnitTests::RailsApplication.new
 $test_app.create
 $test_app.load
 
+require 'active_record/base'
+
 ENV['BUNDLE_GEMFILE'] ||= app.gemfile_path
 ENV['RAILS_ENV'] = 'test'