How to simulate corporate Proxy Server on my development machine

The easiest way I found is:

1. Download and run Fiddler proxy (it's free). It will automatically set itself as a system proxy in Windows on each run. Also click Rules -> Require Proxy Authentication in the top menu if you want to test authentication to the proxy (username and password are "1").

2. Open Windows Firewall, then Advanced settings -> Windows Firewall Properties. Block all outbound connections for all profiles you need (domain, private, public) and click OK.

3. Add new outbound firewall rule to allow all access for 8888 port (default Fiddler port) or "%LOCALAPPDATA%\Programs\Fiddler\Fiddler.exe" app.

That's it, only the programs which use your proxy settings (http://1:[email protected]:8888) will work.

You could have an isolated operating system instance in a virtual machine, which gets access to internet only through a proxy. When you need to test, move the app into the OS inside the virtual machine and see how it behaves.