code: def test_count(self):
      d = fo.Dataset()
      self.assertEqual(d.count(), 0)
  
      v = d.view()
      self.assertEqual(v.count(), 0)
  
      s = fo.Sample(filepath="image.jpeg")
      d.add_sample(s)
      self.assertEqual(d.count(), 1)
      self.assertEqual(v.count(), 1)
  
      s["single"] = fo.Classification()
      s["list"] = fo.Classifications(
          classifications=[
              fo.Classification(label="a"),
              fo.Classification(label="b"),
          ]
      )
      s["empty"] = fo.Classifications()
      s.save()
      self.assertEqual(d.count("single"), 1)
      self.assertEqual(d.count("list.classifications"), 2)
      self.assertEqual(
          d.count(F("list.classifications").filter(F("label") == "a")),
          1,
      )
      self.assertEqual(d.count("empty.classifications"), 0)
  
      d = fo.Dataset()
      s = fo.Sample(filepath="video.mp4")
      s[1]["value"] = "value"
      s[2]["value"] = "value"
      d.add_sample(s)
      self.assertEqual(d.count("frames"), 2)
  
imports: from datetime import date, datetime, timedelta
  import math
  from bson import ObjectId
  import numpy
  import unittest
  import fiftyone
  import fiftyone.core.fields
  from fiftyone import ViewField
  from decorators import drop_datasets
label_desc: Use image node_id 2 for calling the DatasetTests obj's underlying member method code with example usage: obj.test_count() without return types