Not the issue for this commit, but can you do it like this (to remove the intent)?

if c.checkpointManager != nil {
  return nil
}

c.checkpointManager, err := checkpointmanager.NewCheckpointManager(path)
if err != nil {
  return err
}

pods, err := checkpoint.LoadPods(c.checkpointManager)
if err != nil {
  return err
}

updates <- kubetypes.PodUpdate{Pods: pods, Op: kubetypes.RESTORE, Source: kubetypes.ApiserverSource}
return nil

i suggest to use library function checkpoint/WritePod to
write checkpoint, it helps to avoid hard code pod spec in string.

CreateValidPod()
WritePod()

although you need to initialize the checkpointmanager,
this checkpointmanager should not affect restore.

the 3 lines below can be replaced with

channel, ch, config := createPodConfigTester(PodConfigNotificationIncremental)

had to add this because restores were not propogated through to the updates channel

make sense

could you explain a little bit why this is necessary? since createPodConfigTester() does the same thing with channel named "TestSource"

The API server restore get pushed to a channel for "api".

maybe i missed something, correct me if i my understanding is wrong, does this test need a channel named "api" specifically? or any channel name is fine, since the test own the channel, push and get update from it, thanks

correct. The channel needs to be called "api" specifically. The function that is there will only receive on Source: 'test'.

when i looked at the code further, i do think the channel named with test should work unless your actual testing prove it is not.

updates <- kubetypes.PodUpdate{Pods: pods, Op: kubetypes.RESTORE, Source: kubetypes.ApiserverSource}

the value of 'Source' at this line does not matter (is it?), eventually all updates will merged to 'ch',
only need to make sure it matches with source name below which you already did:

expectPodUpdate(t, ch, CreatePodUpdate(kubetypes.RESTORE, kubetypes.ApiserverSource, pod))

the code below should work:

channel, ch, config := createPodConfigTester(PodConfigNotificationIncremental)      
if err := config.Restore(tmpDir, channel); err != nil {     
    t.Fatalf("Restore returned error: %v", err)     
}     
expectPodUpdate(t, ch, CreatePodUpdate(kubetypes.RESTORE, kubetypes.ApiserverSource, pod))    

i could be wrong if actual test prove it, my intention here: we don't have to add new function unless it is really
necessary, thanks.

When I use the existing createPodConfigTester I get the following error:

--- FAIL: TestPodRestore (0.00s)
	config_test.go:118: Expected types.PodUpdate{Pods:[]*v1.Pod(nil), Op:6, Source:"api"}, Got types.PodUpdate{Pods:[]*v1.Pod(nil), Op:6, Source:"test"}

Using this test commandline:

make test-integration GOFLAGS="-v" KUBE_TEST_ARGS="-run TestPodRestore" WHAT=k8s.io/kubernetes/pkg/kubelet/config/

ok, just realize that merge() will actually modify Source in PodUpdate based on channel name,
the code below works fine, i tested it locally:

   channel, ch, config := createPodConfigTester(PodConfigNotificationIncremental)
   if err := config.Restore(tmpDir, channel); err != nil {
       t.Fatalf("Restore returned error: %v", err)
   }
   expectPodUpdate(t, ch, CreatePodUpdate(kubetypes.RESTORE, TestSource, pod))

thanks for the review and tip... I updated the PR with that change.

nit: why not use the BootstrapCheckpointAnnotationKey