storage: add more tests for synced, unsynced for watchable store

This adds more tests on functions that updates synced and unsynced in watchable
store. Preparatory change for https://github.com/coreos/etcd/issues/3848.

storage/watchable_store_test.go

@@ -59,6 +59,132 @@ func TestNewWatcherCancel(t *testing.T) {
 	}
 }
 
+// TestCancelUnsynced tests if running CancelFunc removes watchings from unsynced.
+func TestCancelUnsynced(t *testing.T) {
+	// manually create watchableStore instead of newWatchableStore
+	// because newWatchableStore automatically calls syncWatchers
+	// method to sync watchers in unsynced map. We want to keep watchers
+	// in unsynced to test if syncWatchers works as expected.
+	s := &watchableStore{
+		store:    newStore(tmpPath),
+		unsynced: make(map[*watching]struct{}),
+
+		// to make the test not crash from assigning to nil map.
+		// 'synced' doesn't get populated in this test.
+		synced: make(map[string]map[*watching]struct{}),
+	}
+
+	defer func() {
+		s.store.Close()
+		os.Remove(tmpPath)
+	}()
+
+	// Put a key so that we can spawn watchers on that key.
+	// (testKey in this test). This increases the rev to 1,
+	// and later we can we set the watcher's startRev to 1,
+	// and force watchers to be in unsynced.
+	testKey := []byte("foo")
+	testValue := []byte("bar")
+	s.Put(testKey, testValue)
+
+	w := s.NewWatcher()
+
+	// arbitrary number for watcher
+	watcherN := 100
+
+	// create watcherN of CancelFunc of
+	// synced and unsynced
+	cancels := make([]CancelFunc, watcherN)
+	for i := 0; i < watcherN; i++ {
+		// use 1 to keep watchers in unsynced
+		_, cancel := w.Watch(testKey, true, 1)
+		cancels[i] = cancel
+	}
+
+	for idx := range cancels {
+		cancels[idx]()
+	}
+
+	// After running CancelFunc
+	//
+	// unsynced should be empty
+	// because cancel removes watching from unsynced
+	if len(s.unsynced) != 0 {
+		t.Errorf("unsynced size = %d, want 0", len(s.unsynced))
+	}
+}
+
+// TestSyncWatchings populates unsynced watching map and
+// tests syncWatchings method to see if it correctly sends
+// events to channel of unsynced watchings and moves these
+// watchings to synced.
+func TestSyncWatchings(t *testing.T) {
+	s := &watchableStore{
+		store:    newStore(tmpPath),
+		unsynced: make(map[*watching]struct{}),
+		synced:   make(map[string]map[*watching]struct{}),
+	}
+
+	defer func() {
+		s.store.Close()
+		os.Remove(tmpPath)
+	}()
+
+	testKey := []byte("foo")
+	testValue := []byte("bar")
+	s.Put(testKey, testValue)
+
+	w := s.NewWatcher()
+
+	// arbitrary number for watcher
+	watcherN := 100
+
+	for i := 0; i < watcherN; i++ {
+		// use 1 to keep watchers in unsynced
+		w.Watch(testKey, true, 1)
+	}
+
+	// Before running s.syncWatchings()
+	//
+	// synced should be empty
+	// because we manually populate unsynced only
+	if len(s.synced[string(testKey)]) != 0 {
+		t.Fatalf("synced[string(testKey)] size = %d, want 0", len(s.synced[string(testKey)]))
+	}
+	// unsynced should not be empty
+	// because we manually populated unsynced only
+	if len(s.unsynced) == 0 {
+		t.Errorf("unsynced size = %d, want %d", len(s.unsynced), watcherN)
+	}
+
+	// this should move all unsynced watchings
+	// to synced ones
+	s.syncWatchings()
+
+	// After running s.syncWatchings()
+	//
+	// synced should not be empty
+	// because syncWatchings populates synced
+	// in this test case
+	if len(s.synced[string(testKey)]) == 0 {
+		t.Errorf("synced[string(testKey)] size = 0, want %d", len(s.synced[string(testKey)]))
+	}
+	// unsynced should be empty
+	// because syncWatchings is expected to move
+	// all watchings from unsynced to synced
+	// in this test case
+	if len(s.unsynced) != 0 {
+		t.Errorf("unsynced size = %d, want 0", len(s.unsynced))
+	}
+
+	// All of the watchings actually share one channel
+	// so we only need to check one shared channel
+	// (See watcher.go for more detail).
+	if len(w.(*watcher).ch) != watcherN {
+		t.Errorf("watched event size = %d, want %d", len(w.(*watcher).ch), watcherN)
+	}
+}
+
 func TestUnsafeAddWatching(t *testing.T) {
 	s := newWatchableStore(tmpPath)
 	defer func() {