Groups should not have an execution result.

Changelog.md

@@ -1,6 +1,11 @@
 ### Development
 [Full Changelog](http://github.com/rspec/rspec-core/compare/v3.5.0.beta1...master)
 
+Enhancements:
+
+* Remove unneeded `:execution_result` example groups metadata, saving a
+  bit of memory. (Myron Marston, #2172)
+
 Bug Fixes:
 
 * Prevent a `TypeError` from occuring when running via the rake task when

lib/rspec/core/metadata.rb

@@ -128,7 +128,6 @@ def initialize(metadata, user_metadata, index_provider, description_args, block)
         def populate
           ensure_valid_user_keys
 
-          metadata[:execution_result] = Example::ExecutionResult.new
           metadata[:block]            = block
           metadata[:description_args] = description_args
           metadata[:description]      = build_description_from(*metadata[:description_args])
@@ -219,6 +218,7 @@ def self.create(group_metadata, user_metadata, index_provider, description, bloc
           end)
           group_metadata.update(example_metadata)
 
+          example_metadata[:execution_result] = Example::ExecutionResult.new
           example_metadata[:example_group] = group_metadata
           example_metadata[:shared_group_inclusion_backtrace] = SharedExampleGroupInclusionStackFrame.current_backtrace
           example_metadata.delete(:parent_example_group)

spec/rspec/core/metadata_spec.rb

@@ -141,15 +141,36 @@ def metadata_for(*args)
         end
 
         it 'does not include example-group specific keys' do
-          meta = nil
+          example_meta = nil
+          group_meta = nil
 
           RSpec.describe "group" do
             context "nested" do
-              meta = example("foo").metadata
+              group_meta = metadata
+              example_meta = example("foo").metadata
             end
           end
 
-          expect(meta.keys).not_to include(:parent_example_group)
+          expect(group_meta.keys - example_meta.keys).to contain_exactly(:parent_example_group)
+        end
+      end
+
+      context "for an example group" do
+        it 'does not include example specific keys' do
+          example_meta = nil
+          group_meta = nil
+
+          RSpec.describe "group" do
+            context "nested" do
+              group_meta = metadata
+              example_meta = example("foo").metadata
+            end
+          end
+
+          expect(example_meta.keys - group_meta.keys).to contain_exactly(
+            :execution_result, :last_run_status, :skip,
+            :shared_group_inclusion_backtrace, :example_group
+          )
         end
       end