Site transfer. Are there testing services?

Question

Domain Name System

I often run into problems after migrating sites. Who has the paths not changed, who else has some kind of problem. Also, many people want to test the site BEFORE changing dns zones to a new hosting/server.

At the moment there are two options -
1) Hosting provides a test subdomain (rarely)
2) Using the hosts file (also does not always work and sometimes it is difficult to check whether the site has really started to open from a new server. You cannot check two copies of the site)

Maybe someone knows the service which helps in such cases for testing. For example, I see it like this -

The user wants to test the site on a new hosting after the transfer. He visits such a "service site", enters the domain under test and the IP address of the new server. He is transferred to our "ala anonymizer", which shows him a site on a different IP address. The user can check the operation of the site without prescribing hosts at home. If something does not work, then it is recommended to double-check the operation of the site through hosts

Answer 1

my hoster gives 1 month of free hosting without payment when transferring the site

Answer 2

I think this problem can be solved, but the method is not universal, for example, by downloading recursively through wget links, the source site and the site being tested, then calculate the difference in the space occupied.
But there are downsides - dependence on third-party dynamic banners that can change size.