Yes, you can 
This is what I do:
config/test.exs:
config :app, :api_endpoint, "http://localhost:9999"
In your test:
setup do
bypass = Bypass.open(port: 9999)
...
end
As you can see, by passing the port option, you can tell Bypass which port to use. This allows you to configure the URL globally. This test can now run asynchronously with other tests, as it doesn’t need to overwrite the global test configuration.
I hope this helps.
