Response is not rendered in requests specs with Rails 7.2 and ActiveModelSerializers

[januszm]

What Ruby, Rails and RSpec versions are you using?

Ruby version: 3.2.5
Rails version: 7.2.1
RSpec version: rspec-rails 7.0.1 , rspec-core 3.13.1

Observed behaviour

Before upgrade to Rails 7.1.2, both response and response.parsed_body returned properly rendered JSON for an API that uses Rails ActiveModelSerializers. After the upgrade, response contains the ActiveModelSerializers object simply returned as string, instead of the actual render.

> response
=> ...
 @stream=
  #<ActionDispatch::Response::Buffer:0x0000000135a98810
   @buf=["\"#<ActiveModelSerializers::Adapter::Attributes:0x0000000135add410>\""],

> response.body # or response.parsed_body, same result
=> "#<ActiveModelSerializers::Adapter::Attributes:0x000000012149dd70>"

Expected behaviour

In requests specs, response from a test for an API that uses ActiveModelSerializers and returns JSON, should return properly rendered JSON object, instead it returns the serializer instance.

Can you provide an example reproduction?

I created a brand new Rails 7.2 application with ActiveModelSerializers, but with stadard Rails setup and it properly renders the JSON object in the Integration test

test/integration/api_test.rb:7 ExampleTest#test_api:

    4: def test_api
    5:   Property.create(address: "155 Jackson", city: "Chicago")
    6:   get "/properties"
 => 7:   binding.pry
    8: end

> response
 @stream=
  #<ActionDispatch::Response::Buffer:0x0000000106629100
   @buf=
    ["[{\"address\":\"MyString\",\"city\":\"MyString\"},{\"address\":\"123 Jackson\",\"city\":\"Chicago\"}]"],

> response.parsed_body
=> [{"address"=>"MyString", "city"=>"MyString"}, {"address"=>"155 Jackson", "city"=>"Chicago"}]

which proves this is not an issue with ActiveModelSerializers, because it produces proper results with standard Rails 7.2.1 test suite. Not sure if this is an issue with rspec-rails or another gem from rspec group, so posting it here.