Skip testing default gems on rubies without them

Ruby 1.9.3 and earlier do not have default gems but Rake tests tried to
use them leading to an error.

Now the test using default gems is skipped when default gems are not
present.

Fixes #8

History.rdoc

@@ -6,6 +6,7 @@ Bug fixes:
   task.  Pull requset #9 by Matt Palmer.
 * Documented how Rake::DSL#desc handles sentences in task descriptions.
   Issue #7 by Raza Sayed.
+* Fixed test error on 1.9.3 with legacy RubyGems.  Issue #8 by Matt Palmer.
 * Deleted duplicated History entry.  Pull request #10 by Yuji Yamamoto.
 
 === 10.4.1 / 2014-12-01

test/test_rake_test_task.rb

@@ -97,17 +97,22 @@ def test_run_code_rake
   end
 
   def test_run_code_rake_default_gem
+    skip 'this ruby does not have default gems' unless
+      Gem::Specification.method_defined? :default_specifications_dir
+
     default_spec = Gem::Specification.new 'rake', 0
     default_spec.loaded_from = File.join Gem::Specification.default_specifications_dir, 'rake-0.gemspec'
-    rake, Gem.loaded_specs['rake'] = Gem.loaded_specs['rake'], default_spec
+    begin
+      rake, Gem.loaded_specs['rake'] = Gem.loaded_specs['rake'], default_spec
 
-    test_task = Rake::TestTask.new do |t|
-      t.loader = :rake
-    end
+      test_task = Rake::TestTask.new do |t|
+        t.loader = :rake
+      end
 
-    assert_match(/\A(-I".*?" *)* ".*?"\Z/, test_task.run_code)
-  ensure
-    Gem.loaded_specs['rake'] = rake
+      assert_match(/\A(-I".*?" *)* ".*?"\Z/, test_task.run_code)
+    ensure
+      Gem.loaded_specs['rake'] = rake
+    end
   end
 
   def test_run_code_testrb_ruby_1_8_2