Cargo test failure on macOS

[jopemachine]

After #157, the cargo test command fails on macOS with an AddrNotAvailable error because only 127.0.0.1 is assigned as the loopback address by default on macOS.

As a workaround, by running the script below to assign all 127.0.0.x addresses as loopback, we can make the test code work properly on macOS as well.

./misc/setup-loopback-addresses.sh

Since this configuration resets after a reboot, we need to rerun the script.
It would be better to find a solution that doesn't require running the script every time.