code: def test_add_dim():
      domain = Domain((1,), (1.0,))
      a = OnGrid(jnp.asarray([[1.0]]), domain)
  
      b = a.add_dim()
  
      # It must have three axis: [new_dim, old_dim, 1 (for scalar fields)]
      assert b.params.shape == (1, 1, 1)
  
imports: import pytest
  from jax import jit
  from jax import numpy
  from jax import random
  from jaxdf.discretization import FiniteDifferences, FourierSeries, OnGrid
  from jaxdf.geometry import Domain
  from jaxdf.operators import inverse
label_desc: Use image node_id 16 for calling a global function with example usage: test_add_dim() without return types