code: def test_define():
      expr = sympy.exp(3 * t)
      assert str(expr) == "exp(3*t)"
      newf = define("f", expr)
      assert str(newf) == "f(t)"
      f = lambdify_t(newf)
      tval = np.random.standard_normal((3,))
      assert_almost_equal(np.exp(3 * tval), f(tval))
  
imports: import re
  import numpy
  import pytest
  import sympy
  from numpy.testing import assert_almost_equal, assert_array_almost_equal, assert_array_equal
  from sympy import DiracDelta, Dummy, Function, Symbol
  from sympy.utilities.lambdify import implemented_function, lambdify
  from nipy.algorithms.statistics.formula import Term
  from ..None import hrf
  from ..utils import Interp1dNumeric, TimeConvolver, blocks, convolve_functions, define, events, interp, lambdify_t, linear_interp, step_function
label_desc: Use image node_id 1 for calling a global function with example usage: test_define() without return types