E2E tests fail with go 1.13

[chaodaiG]

When running serving tests with go1.13, they would fail complaining flags provided but not defined.
For example:

# clone knative/serving
go test -v -tags=e2e -count=1 ./test/e2e -run ^TestAutoscaleUpDownUp$

Got errors:

flag provided but not defined: -test.v

[chaodaiG]

/assign @steuhs

[srinivashegde86]

probably related - golang/go#31859

[adrcunha]

This seems to be caused due to the way flags are parsed in serving/test/e2e:

$ go test -v -count=1 ./pkg/... -run ^TestAutoscaleUpDownUp$
testing: warning: no tests to run
PASS
ok      knative.dev/serving/pkg/activator       0.294s [no tests to run]
?       knative.dev/serving/pkg/activator/config        [no test files]
testing: warning: no tests to run
...
$ go test -v -tags=e2e -count=1 ./test/e2e -run ^TestAutoscaleUpDownUpX$
flag provided but not defined: -test.v
Usage of /tmp/go-build413005213/b001/e2e.test:
...

[adrcunha]

We're running go 1.12 on Prow. The issue described happens with go 1.13rc1.

[adrcunha]

istio is facing the same issue: istio/istio#16797

[adrcunha]

Root cause: custom flag initialization function (https://github.com/knative/serving/blob/master/test/e2e_flags.go#L66) calling flag.Parse before the testing flags have been registered.

It seems to me that simply omitting flag.Parse() would work, as it will be called later by the testing package.

[howardjohn]

We fixed a similar issue in Istio by parsing in test main instead of init fwiw

[adrcunha]

Interesting, thanks John. @steuhs if we go that way, make sure test-infra is updated because otherwise using TestMain might break the presubmit build tests depending on what it does or expects.

[chaodaiG]

@steuhs is OOO this week
/assign

[chaodaiG]

/unassign @steuhs

[chaodaiG]

In go1.13 testing level flags (i.e. -v) are registered in testing.Init() according to release note as part of generated main() function, which is executed later than global variable initialization, such as initializeServingFlags call, which failed to parse flags as they are not registered yet.