Stash methods that get and set thread local variables to allow the user to mock them

lib/rspec/support.rb

@@ -90,14 +90,23 @@ def self.class_of(object)
       singleton_class.ancestors.find { |ancestor| !ancestor.equal?(singleton_class) }
     end
 
-    # A single thread local variable so we don't excessively pollute that namespace.
+    # Stash original methods to allow the user to mock them.
     if RUBY_VERSION.to_f >= 2
+      THREAD_VARIABLE_GET = Thread.instance_method(:thread_variable_get)
+      THREAD_VARIABLE_SET = Thread.instance_method(:thread_variable_set)
+    else
+      THREAD_VARIABLE_GET = Thread.instance_method(:[])
+      THREAD_VARIABLE_SET = Thread.instance_method(:[]=)
+    end
+
+    # A single thread local variable so we don't excessively pollute that namespace.
+    if RUBY_VERSION >= '2.7'
       def self.thread_local_data
-        Thread.current.thread_variable_get(:__rspec) || Thread.current.thread_variable_set(:__rspec, {})
+        THREAD_VARIABLE_GET.bind_call(Thread.current, :__rspec) || THREAD_VARIABLE_SET.bind_call(Thread.current, :__rspec, {})
       end
     else
       def self.thread_local_data
-        Thread.current[:__rspec] ||= {}
+        THREAD_VARIABLE_GET.bind(Thread.current).call(:__rspec) || THREAD_VARIABLE_SET.bind(Thread.current).call(:__rspec, {})
       end
     end
 

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