code: def test_file_plugin_loaded(self):
      plugins_root = self.FIXTURES_ROOT / "plugins"
  
      sys.argv = ["allennlp"]
  
      available_plugins = set(discover_plugins())
      assert available_plugins == set()
  
      with pushd(plugins_root):
          main()
          subcommands_available = Subcommand.list_available()
          assert "d" in subcommands_available
  
file_path: allennlp/tests/commands/main_test.py
imports: import shutil
  import sys
  import pytest
  from allennlp.commands import main
  from allennlp.commands.subcommand import Subcommand
  from allennlp.common.checks import ConfigurationError
  from allennlp.common.plugins import discover_plugins
  from allennlp.common.testing import AllenNlpTestCase
  from allennlp.common.util import push_python_path, pushd
label_desc: Use image node_id 4 for calling the TestMain obj's underlying member method code with example usage: obj.test_file_plugin_loaded() without return types