Question : Problem: Enabling and Disablingl NICs in a windows desktop machine

I have a requirement where the 3 NIC cards attached to the Desktop should be active so that I can enable or disable them on the fly without physically touching the machine (atleast 2 Physical NICs active at a time) . The reason being is that we generate automated tests across two different types of network (assume Network A  and Network B).  Network A simulates certain error conditions in the network and Network B is regular production network. The test has to be executed against both the networks (only one network active at a time). Is there a possiblity to enable or disable NICs . Assuming that we install 3 physical NICs (NIC-A, NIC-B and NIC-C). NIC-A connects to Network A, NIC-B connects to Network B and NIC-C will have a permanent IP address through which the admin user can connect to the machine remotely. Is it possible to connect to the desktop machine in which 2 NICs are installed through remote desktop connection (through NIC-C) and enable/disable the NICs (NIC-A or NIC-B) and run a test against one network at a time without physically touching the machine. The reason being is that the desktop will be deployed in the datacenter which we won't have building access), any help is greatly appreciated.

Answer : Problem: Enabling and Disablingl NICs in a windows desktop machine

The subnet and or gateway will determine what network adapter is used.

You cannot have 2 gateways, but you can have a route to one gateway for specific traffic, i.e your remote connection, and other traffic would use the default gateway.

As for local traffic, if you are going to have 2 network adapters on the same subnet such as 192.168.1.100 and 192.168.1.200 you will have problems, you will not be able to control the direction the traffic takes. Although I suppose you could create a default route using 0.0.0.0 and specifying the network adapter.
You do run the risk of loosing connectivity if you try to force traffic through  A or B and try to still maintain access through C.

Have you considered using virtual machines or a virtual network? You could remotely logon to the host machine and then safely manage the Virtual machines and change their addressing and enable/disable adapters at will using a GUI.