code: def test_not_string(self):
      metrics = {"test": {"hello": 2}}
      res = torchbearer.callbacks.printer._format_metrics(
          metrics, lambda x: round(x, 3)
      )
      self.assertEqual(res, "test={'hello': 2}")
  
file_path: torchbearer/tests/callbacks/test_printer.py
imports: from unittest import TestCase
  from mock import patch, MagicMock
  import torchbearer
  from torchbearer.callbacks import Tqdm, ConsolePrinter
label_desc: Use image node_id 3 for calling the TestFormatMetrics obj's underlying member method code with example usage: obj.test_not_string() without return types