Add test to warn about search being deprecated

test/stripe/api_operations_test.rb

@@ -39,6 +39,26 @@ def self.protected_fields
       end
     end
 
+    context ".search" do
+      should "warn that ._search is deprecated" do
+        old_stderr = $stderr
+        $stderr = StringIO.new
+        begin
+          stub_request(:post, "#{Stripe.api_base}/v1/customers/search?query=foo:bar")
+            .to_return(body: JSON.generate(object: "customer"))
+
+          client = StripeClient.new
+          client.request { Customer._search("/v1/customers/search", query: "foo:bar") }
+
+          message = "NOTE: Stripe::Customer._search is deprecated; use request_stripe_object " \
+                    "instead. It will be removed on or after 2024-01."
+          assert_match Regexp.new(message), $stderr.string
+        ensure
+          $stderr = old_stderr
+        end
+      end
+    end
+
     context ".nested_resource_class_methods" do
       class MainResource < APIResource # rubocop:todo Lint/ConstantDefinitionInBlock
         extend Stripe::APIOperations::NestedResource