Switch rspec local data to a thread accessor

lib/rspec/support.rb

@@ -1,5 +1,9 @@
 # frozen_string_literal: true
 
+class Thread
+  attr_accessor :__rspec_local_data
+end
+
 module RSpec
   module Support
     # @api private
@@ -91,14 +95,8 @@ def self.class_of(object)
     end
 
     # A single thread local variable so we don't excessively pollute that namespace.
-    if RUBY_VERSION.to_f >= 2
-      def self.thread_local_data
-        Thread.current.thread_variable_get(:__rspec) || Thread.current.thread_variable_set(:__rspec, {})
-      end
-    else
-      def self.thread_local_data
-        Thread.current[:__rspec] ||= {}
-      end
+    def self.thread_local_data
+      Thread.current.__rspec_local_data ||= {}
     end
 
     # @api private

spec/rspec/support_spec.rb

@@ -204,6 +204,17 @@ def object.some_method
           end.resume
         end
       end
+
+      it "works when Thread#thread_variable_get and Thread#thread_variable_set are mocked" do
+        expect(Thread.current).to receive(:thread_variable_set).with(:test, true).once.and_return(true)
+        expect(Thread.current).to receive(:thread_variable_get).with(:test).once.and_return(true)
+
+        Thread.current.thread_variable_set(:test, true)
+        expect(Thread.current.thread_variable_get(:test)).to eq true
+
+        RSpec::Support.thread_local_data[:__for_test] = :oh_hai
+        expect(RSpec::Support.thread_local_data[:__for_test]).to eq :oh_hai
+      end
     end
 
     describe "failure notification" do