code: def test_concatenate():
      assert_array_equal(
          c(1, np.zeros(3)), np.array([1.0, 0.0, 0.0, 0.0])
      )
      assert_array_equal(
          c([1], np.zeros(3)), np.array([1.0, 0.0, 0.0, 0.0])
      )
      assert_array_equal(c(1), np.ones(1))
      assert c() is None
      assert_array_equal(c([1]), np.ones(1))
  
imports: from pmdarima.utils.array import diff, diff_inv, c, is_iterable, as_series, check_exog, check_endog
  from pmdarima.utils import get_callable
  from numpy.testing import assert_array_equal, assert_array_almost_equal
  import datetime
  import pytest
  import pandas
  import numpy
label_desc: Use image node_id 5 for calling a global function with example usage: test_concatenate() without return types