... and that's a quite big no-no, especially in JS land 😕

Consider this use case (we have a similar situation as we speak):
There is a package X using stellar-sdk and a package Y using stellar-sdk as well, but a slightly different version.

If Y is a dependency of X or if X and Y are both being used in another package Z then we will end up with a nasty situation. The Network singleton that X imports from stellar-sdk/stellar-base won't be the same instance that Y has, since they each depend on a different version (two different stellar-base in the node_modules/ tree).

Thus you can run Network.useTestNetwork() in X and still get a No network selected. error in Y. Same happens when npm link-ing packages during development, even if all packages require the same version.

Proposal

Is there actually a need to have this stateful Network singleton? I would favor a solution based on passing the pubnet/testnet switch to the Server constructor, since horizon servers won't suddenly change the network they are running on.

import { Network, Server } from 'stellar-base'

const horizon = new Server('https://horizon-testnet.stellar.org/', { network: Network.testnet() })

Sorry for the wall of text 😉