[3.4] avoid closing a watch with ID 0 incorrectly

[kafuu-chino]

Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

This PR backports #14296 to release-3.4. cc @ahrtr @mitake

[kafuu-chino]

@ahrtr @mitake I found unable to use Assert in 3.4 and use panic instead. Please help to confirm whether there will be any problem.

[ahrtr]

Thanks @kafuu-chino for backporting the PR.

Unfortunately, release-3.4 doesn't have integration test at all, so you have to remove the integration test case for now.

[ahrtr]

Please try to manually verify this PR indeed fixes the issue, thx

[kafuu-chino]

Please try to manually verify this PR indeed fixes the issue, thx

In my local test, the token expires and watch can trigger normally.

[ahrtr]

LGTM

Thank you @kafuu-chino

[ahrtr]

cc @mitake @spzala to double confirm

[mitake]

@ahrtr @kafuu-chino I think just the path of integration test is different in release-3.4, and we can backport the test case like this? https://github.com/etcd-io/etcd/pull/14548/files#diff-93bc434c49bed544fa4df1bd0750fb22f98c12da81c75f8026520b4eed986108

[ahrtr]

@ahrtr @kafuu-chino I think just the path of integration test is different in release-3.4, and we can backport the test case like this? https://github.com/etcd-io/etcd/pull/14548/files#diff-93bc434c49bed544fa4df1bd0750fb22f98c12da81c75f8026520b4eed986108

Thanks @mitake for the reminder. release-3.4 indeed has integration test, and paths are as below,

etcd/test

Lines 185 to 188 in de11726

	INTEGTESTPKG=("${REPO_PATH}/integration"
	"${REPO_PATH}/client/integration"
	"${REPO_PATH}/clientv3/integration"
	"${REPO_PATH}/contrib/raftexample"

[kafuu-chino]

@ahrtr @kafuu-chino I think just the path of integration test is different in release-3.4, and we can backport the test case like this? https://github.com/etcd-io/etcd/pull/14548/files#diff-93bc434c49bed544fa4df1bd0750fb22f98c12da81c75f8026520b4eed986108

Thanks @mitake for the reminder. release-3.4 indeed has integration test, and paths are as below,

etcd/test

Lines 185 to 188 in de11726

	INTEGTESTPKG=("${REPO_PATH}/integration"
	"${REPO_PATH}/client/integration"
	"${REPO_PATH}/clientv3/integration"
	"${REPO_PATH}/contrib/raftexample"

ok, I'll take a look today.

[kafuu-chino]

Integration test has been added. @ahrtr @mitake

[mitake]

LGTM, thanks @kafuu-chino @ahrtr !