change Thread.sleep to waitUntil function under test files

[JacobCho-i]

Issue #, if available:
#1028

Description of changes:
replaced Thread.sleep functions with waitUntil function in tests under src/test files

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[lezzago]

Instead of false, we would want to verifyMonitorStats. That way we get the benefit of the waitUtil function

[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/alerting/backport-2.x 2.x
# Navigate to the new working tree
pushd ../.worktrees/alerting/backport-2.x
# Create a new branch
git switch --create backport-1242-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 a26f4c087fbeae4fb79fd598b8c5cf46ecf11f55
# Push it to GitHub
git push --set-upstream origin backport-1242-to-2.x
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/alerting/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport-1242-to-2.x.

[AWSHurneyt]

@JacobCho-i Looks like the automatic backport failed for this PR. Could you checkout a fork of the 2.x branch, cherry-pick your changes to it, and create another PR directly to the 2.x branch? There were likely some merge conflicts that occurred that caused the backport to fail.

[AWSHurneyt]

@JacobCho-i Looks like the automatic backport failed for this PR. Could you checkout a fork of the 2.x branch, cherry-pick your changes to it, and create another PR directly to the 2.x branch? There were likely some merge conflicts that occurred that caused the backport to fail.

Manual backport PR #1301