code: def test_drop_columns(self):
      t = self.t_env.from_elements(
          [(1, "Hi", "Hello")], ["a", "b", "c"]
      )
      result = t.drop_columns(t.a, t.c)
      query_operation = result._j_table.getQueryOperation()
      self.assertEqual(
          "[b]", query_operation.getProjectList().toString()
      )
  
imports: from pyflink.testing.test_case_utils import PyFlinkStreamTableTestCase
label_desc: Use image node_id 4 for calling the StreamTableColumnsOperationTests obj's underlying member method code with example usage: obj.test_drop_columns() without return types