Removed the AS core_ext/kernel/debugger breakpoint method as this method is added by ruby-debug and should be left as is. Missing tests added.

activesupport/lib/active_support/core_ext/kernel/debugger.rb

@@ -5,12 +5,6 @@ module Kernel
       message = "\n***** Debugger requested, but was not available (ensure ruby-debug is listed in Gemfile/installed as gem): Start server with --debugger to enable *****\n"
       defined?(Rails) ? Rails.logger.info(message) : $stderr.puts(message)
     end
-  end
-
-  undef :breakpoint if respond_to?(:breakpoint)
-  def breakpoint
-    message = "\n***** The 'breakpoint' command has been renamed 'debugger' -- please change *****\n"
-    defined?(Rails) ? Rails.logger.info(message) : $stderr.puts(message)
-    debugger
+    alias breakpoint debugger unless respond_to?(:breakpoint)
   end
 end

activesupport/test/core_ext/kernel_test.rb

@@ -52,10 +52,10 @@ class KernelTest < Test::Unit::TestCase
     class << o; @x = 1; end
     assert_equal 1, o.class_eval { @x }
   end
-  
+
   def test_capture
-    assert_equal 'STDERR', capture(:stderr) {$stderr.print 'STDERR'}
-    assert_equal 'STDOUT', capture(:stdout) {print 'STDOUT'}
+    assert_equal 'STDERR', capture(:stderr) { $stderr.print 'STDERR' }
+    assert_equal 'STDOUT', capture(:stdout) { print 'STDOUT' }
   end
 end
 
@@ -73,3 +73,43 @@ class KernelSuppressTest < Test::Unit::TestCase
     suppress(LoadError, ArgumentError) { raise ArgumentError }
   end
 end
+
+class MockStdErr
+  attr_reader :output
+  def puts(message)
+    @output ||= []
+    @output << message
+  end
+
+  def info(message)
+    puts(message)
+  end
+
+  def write(message)
+    puts(message)
+  end
+end
+
+class KernelDebuggerTest < Test::Unit::TestCase
+  def test_debugger_not_available_message_to_stderr
+    old_stderr = $stderr
+    $stderr = MockStdErr.new
+    debugger
+    assert_match(/Debugger requested/, $stderr.output.first)
+  ensure
+    $stderr = old_stderr
+  end
+
+  def test_debugger_not_available_message_to_rails_logger
+    rails = Class.new do
+      def self.logger
+        @logger ||= MockStdErr.new
+      end
+    end
+    Object.const_set("Rails", rails)
+    debugger
+    assert_match(/Debugger requested/, rails.logger.output.first)
+  ensure
+    Object.send(:remove_const, "Rails")
+  end
+end