Without this, any test relying on underlying use of magicsock will fail
without network connectivity, even when the test logic has no need for a
network connection. Tests currently in this bucket include many in
tstest/integration and in tsnet.
Further explanation:
ipn only becomes Running when it sees at least one live peer or DERP
connection:
0cc1b2ff76/ipn/ipnlocal/local.go (L5861-L5866)
When tests only use a single node, they will never see a peer, so the
node has to wait to see a DERP server.
magicsock sets the preferred DERP server in updateNetInfo(), but this
function returns early if the network is down.
0cc1b2ff76/wgengine/magicsock/magicsock.go (L1053-L1106)
Because we're checking the real network, this prevents ipn from entering
"Running" and causes the test to fail or hang.
In tests, we can assume the network is up unless we're explicitly testing
the behaviour of tailscaled when the network is down. We do something similar
in magicsock/derp.go, where we assume we're connected to control unless
explicitly testing otherwise:
7d2101f352/wgengine/magicsock/derp.go (L166-L177)
This is the template for the changes to `networkDown()`.
Fixes#17122
Co-authored-by: Alex Chan <alexc@tailscale.com>
Signed-off-by: Harry Harpham <harry@tailscale.com>
61ac021c5d