Add spec to the result of Coverage lib for begin

Ref: jruby/jruby#8173
This commit is intended to make sure `Coverage` library behaves
the same for the code with `begin`. JRuby had an issue so this
change will help JRuby and other implementations to avoid it.

library/coverage/fixtures/code_with_begin.rb

@@ -0,0 +1,3 @@
+begin
+  'coverage with begin'
+end

library/coverage/result_spec.rb

@@ -6,6 +6,7 @@
     @class_file = fixture __FILE__, 'some_class.rb'
     @config_file = fixture __FILE__, 'start_coverage.rb'
     @eval_code_file = fixture __FILE__, 'eval_code.rb'
+    @with_begin_file = fixture __FILE__, 'code_with_begin.rb'
   end
 
   before :each do
@@ -16,6 +17,7 @@
     $LOADED_FEATURES.delete(@class_file)
     $LOADED_FEATURES.delete(@config_file)
     $LOADED_FEATURES.delete(@eval_code_file)
+    $LOADED_FEATURES.delete(@with_begin_file)
 
     Coverage.result if Coverage.running?
   end
@@ -354,4 +356,16 @@
 
     Coverage.peek_result.should == result
   end
+
+  it 'covers 100% lines with begin' do
+    Coverage.start
+    require @with_begin_file.chomp('.rb')
+    result = Coverage.result
+
+    result.should == {
+      @with_begin_file => [
+        nil, 1, nil
+      ]
+    }
+  end
 end