RSpec/InstanceVariable. Optimize #on_block callback

lib/rubocop/cop/rspec/instance_variable.rb

@@ -47,13 +47,11 @@ module RSpec
       #   end
       #
       class InstanceVariable < Cop
+        include RuboCop::RSpec::TopLevelGroup
+
         MSG = 'Avoid instance variables – use let, ' \
               'a method call, or a local variable (if possible).'
 
-        EXAMPLE_GROUP_METHODS = ExampleGroups::ALL + SharedGroups::ALL
-
-        def_node_matcher :spec_group?, EXAMPLE_GROUP_METHODS.block_pattern
-
         def_node_matcher :dynamic_class?, <<-PATTERN
           (block (send (const nil? :Class) :new ...) ...)
         PATTERN
@@ -69,9 +67,7 @@ class InstanceVariable < Cop
 
         def_node_search :ivar_assigned?, '(ivasgn % ...)'
 
-        def on_block(node)
-          return unless spec_group?(node)
-
+        def on_top_level_group(node)
           ivar_usage(node) do |ivar, name|
             next if valid_usage?(ivar)
             next if assignment_only? && !ivar_assigned?(node, name)

spec/rubocop/cop/rspec/instance_variable_spec.rb

@@ -152,5 +152,18 @@ def serialize
         end
       RUBY
     end
+
+    it 'flags an instance variable when it is also assigned in sibling example group' do
+      expect_offense(<<-RUBY)
+        describe MyClass do
+          context 'foo' do
+            before { @foo = [] }
+          end
+
+          it { expect(@foo).to be_empty }
+                      ^^^^ Avoid instance variables – use let, a method call, or a local variable (if possible).
+        end
+      RUBY
+    end
   end
 end