How to add eth1 to test device tree?

[Ehsan Mohandesi]

Hi All,
When running the sandbox tests, I want to know how to enable eth1 in order to be able to test network features.
The following command is used to run sandbox tests.
./test/py/test.py -k testname.py
I am specifically interested in running the network tests.
./test/py/test.py -k test_net.py
These Python tests use test.dts device tree which does not have eth1 in it. I can replace the test.dts file with sandbox.dts to enable eth1 and run the network tests; however, I think there should be a better way to do it.
Can anyone help me with this issue?
When running U-Boot, the -T option could be used to tell it to use the test.dts or -D to use sandbox.dts; however, there is no such option when running test.py.
Eth1 is needed in order to enable the network. Enabling the sandbox network is explained after line 250 in doc/arch/sandbox.rst.
For more information, the following is the list of network interfaces when each device tree is used.

arch/sandbox/dts/sandbox.dts
Net:   eth0: host_lo, eth1: host_eth0, eth2: host_br1, eth3: eth at 10002000

arch/sandbox/dts/test.dts
Net:   eth0: eth at 10002000, eth5: eth at 10003000, eth3: sbe5, eth6: eth at 10004000, eth4: dsa-test-eth, eth2: lan0, eth7: lan1