tstest/integration/integration_test.go#TestNATPing seems flakey

[irbekrm]

What is the issue?

TestNATPing errored on an unrelated PR

ok	tailscale.com/wgengine/magicsock
=== RUN   TestNATPing
=== PAUSE TestNATPing
=== CONT  TestNATPing
    integration_test.go:1164: DERP httpsrv listener: 127.0.0.1:42215
    integration_test.go:1196: control URL: http://127.0.0.1:43163/
    integration_test.go:853: Running /tmp/3888925650/tailscale --socket=/tmp/TestNATPing2115165917/001/tailscale.sock up --login-server=http://127.0.0.1:43163/ --reset ...
    integration_test.go:853: Running /tmp/3888925650/tailscale --socket=/tmp/TestNATPing2115165917/006/tailscale.sock up --login-server=http://127.0.0.1:43163/ --reset ...
=== RUN   TestNATPing/v6=false/no_nat
--- PASS: TestNATPing/v6=false/no_nat (0.07s)
=== RUN   TestNATPing/v6=false/n1_has_external_ip
--- PASS: TestNATPing/v6=false/n1_has_external_ip (0.10s)
=== RUN   TestNATPing/v6=false/n2_has_external_ip
--- PASS: TestNATPing/v6=false/n2_has_external_ip (0.06s)
=== RUN   TestNATPing/v6=false/both_have_external_ips
--- PASS: TestNATPing/v6=false/both_have_external_ips (0.04s)
    integration_test.go:1164: DERP httpsrv listener: 127.0.0.1:36809
    integration_test.go:1196: control URL: http://127.0.0.1:42857/
    integration_test.go:853: Running /tmp/3888925650/tailscale --socket=/tmp/TestNATPing2115165917/037/tailscale.sock up --login-server=http://127.0.0.1:42857/ --reset ...
    integration_test.go:853: Running /tmp/3888925650/tailscale --socket=/tmp/TestNATPing2115165917/042/tailscale.sock up --login-server=http://127.0.0.1:42857/ --reset ...
=== RUN   TestNATPing/v6=true/no_nat
    integration_test.go:953: exit status 1
--- FAIL: TestNATPing/v6=true/no_nat (10.03s)
=== RUN   TestNATPing/v6=true/n1_has_external_ip
    integration_test.go:953: exit status 1
--- FAIL: TestNATPing/v6=true/n1_has_external_ip (10.03s)
=== RUN   TestNATPing/v6=true/n2_has_external_ip
    integration_test.go:953: exit status 1
--- FAIL: TestNATPing/v6=true/n2_has_external_ip (10.03s)
=== RUN   TestNATPing/v6=true/both_have_external_ips
    integration_test.go:953: exit status 1
--- FAIL: TestNATPing/v6=true/both_have_external_ips (10.03s)
    stuntest.go:63: STUN server shutdown
    stuntest.go:63: STUN server shutdown
--- FAIL: TestNATPing (45.15s)
FAIL	tailscale.com/tstest/integration
ok	tailscale.com/prober

[agottardo]

I have also noticed this.