Don't overflow stack if method expectation for #respond_to? fails

In the process of generating the error message for a failed method expectation,
ErrorGenerator would call Array#join on an array which contained the receiver.
Internally, Array#join calls #respond_to?(:to_str) on the objects which are being
joined into a string.

If the method expectation was for #respond_to?, the internal call to #respond_to?
could cause the expectation to fail again, causing an infinite loop and resulting
stack overflow.

Avoid this by not using Array#join to generate the error message. Fixes #1020.

lib/rspec/mocks/error_generator.rb

@@ -69,12 +69,7 @@ def raise_similar_message_args_error(expectation, args_for_multiple_calls, backt
       end
 
       def default_error_message(expectation, expected_args, actual_args)
-        [
-          intro,
-          "received",
-          expectation.message.inspect,
-          unexpected_arguments_message(expected_args, actual_args),
-        ].join(" ")
+        "#{intro} received #{expectation.message.inspect} #{unexpected_arguments_message(expected_args, actual_args)}"
       end
 
       # rubocop:disable Style/ParameterLists

spec/rspec/mocks/matchers/receive_spec.rb

@@ -393,6 +393,27 @@ def receiver.method_missing(*a); end # a poor man's stub...
             reset_all
           end
         end
+
+        context "when expected message is respond_to?" do
+          context "and conditions are placed on expected call" do
+            context "and the conditions fail... :(" do
+              it "does not result in infinite recursion and stack overflow" do
+                # Setting a method expectation causes the method to be proxied
+                # RSpec may call #respond_to? when processing a failed expectation
+                # If those internal calls go to the proxied method, that could
+                #   result in another failed expectation error, causing infinite loop
+
+                expect {
+                  obj = Object.new
+                  expect(obj).to receive(:respond_to?).with('something highly unlikely')
+                  obj.respond_to?(:not_what_we_wanted)
+                }.to raise_error(/received :respond_to\? with unexpected arguments/)
+
+                reset_all
+              end
+            end
+          end
+        end
       end
 
       describe "expect_any_instance_of(...).to receive" do