retry.UntilSuccessOrFail(t, func() error {
			if err := checkResult(resultFile, expectedOutputFile); err == nil {
				// We should have waited for the delayed conf
				return fmt.Errorf("did not wait for valid config file")
			}
			return nil
		}, retry.Delay(time.Millisecond), retry.Timeout(time.Millisecond*250))
		var destFilenm string
		if preConfFile != "" {
			destFilenm = preConfFile
		} else {

  // PreStop hook is executed. Regardless of the outcome of the handler, the
  // container will eventually terminate within the Pod's termination grace
  // period (unless delayed by finalizers). Other management of the container blocks until the hook completes
  // or until the termination grace period is reached.

				if len(c.delayedConfName) > 0 {
					// Delayed case
					// Write delayed CNI config file
					data, err := os.ReadFile(filepath.Join("testdata", c.delayedConfName))
					if err != nil {
						t.Fatal(err)
					}
					err = os.WriteFile(filepath.Join(tempDir, c.delayedConfName), data, 0o644)
					if err != nil {
						t.Fatal(err)
					}
					t.Logf("delayed write to %v", filepath.Join(tempDir, c.delayedConfName))

Typically, the whole `kclient.Client` is used,though.

Functionality offered by `kclient` includes:
* Typed clients (via generics) and more ergonomic APIs
* Ability to make a _delayed_ client. This is used when making clients based on CRDs that may not exist.
  In general, Istio does not fail on missing CRDs and prefers to treat these as if there were just zero resources for that client.

                                  type: number
                              type: object
                          type: object
                        delay:
                          description: Delay requests before forwarding, emulating
                            various failures such as network issues, overloaded upstream
                            service, etc.
                          oneOf:

      #
      # If the probe is enabled, it is recommended to have delay=0s,period=15s,failureThreshold=4.
      # This ensures the pod is marked ready immediately after the startup probe passes (which has a 1s poll interval),
      # and doesn't spam the readiness endpoint too much
      #
      # If the probe is disabled, it is recommended to have delay=1s,period=2s,failureThreshold=30.

DOWNLOAD_COMMAND=""
function set_download_command () {
  # Try curl.
  if command -v curl > /dev/null; then
    if curl --version | grep Protocols  | grep https > /dev/null; then
      DOWNLOAD_COMMAND="curl -fLSs --retry 5 --retry-delay 1 --retry-connrefused"
      return
    fi
    echo curl does not support https, will try wget for downloading files.
  else
    echo curl is not installed, will try wget for downloading files.
  fi

  # Try wget.

                                  type: number
                              type: object
                          type: object
                        delay:
                          description: Delay requests before forwarding, emulating
                            various failures such as network issues, overloaded upstream
                            service, etc.
                          oneOf:

DOWNLOAD_COMMAND=""
function set_download_command () {
  # Try curl.
  if command -v curl > /dev/null; then
    if curl --version | grep Protocols  | grep https > /dev/null; then
      DOWNLOAD_COMMAND="curl -fLSs --retry 5 --retry-delay 1 --retry-connrefused"
      return
    fi
    echo curl does not support https, will try wget for downloading files.
  else
    echo curl is not installed, will try wget for downloading files.
  fi

  # Try wget.

function log() {
  echo -e "$(date -u '+%Y-%m-%dT%H:%M:%S.%NZ')\t$*"
}

function retry() {
  local n=1
  local max=5
  local delay=5
  while true; do
    "$@" && break
    if [[ $n -lt $max ]]; then
      ((n++))
      log "Command failed. Attempt $n/$max:"
      sleep $delay;
    else
      log "The command has failed after $n attempts."  >&2
      return 2
    fi
  done
}