code: def test_calculate_dwell_time():
      # Test dwell time calculation
      # This tests only that the calculation does what it appears to; needs some
      # external check
      assert_almost_equal(
          calculate_dwell_time(3.3, 2, 3), 3.3 / (42.576 * 3.4 * 3 * 3)
      )
      # Echo train length of 1 is valid, but returns 0 dwell time
      assert_almost_equal(calculate_dwell_time(3.3, 1, 3), 0)
      with pytest.raises(MRIError):
          calculate_dwell_time(3.3, 0, 3.0)
      with pytest.raises(MRIError):
          calculate_dwell_time(3.3, 2, -0.1)
  
imports: import pytest
  from numpy.testing import assert_almost_equal
  from ..mriutils import MRIError, calculate_dwell_time
label_desc: Use image node_id 1 for calling a global function with example usage: test_calculate_dwell_time() without return types