text: from sympy import symbols, erf, nan, oo, Float, sqrt, pi, O
  
  x, y = symbols('x,y')
  
  def test_erf():
      assert erf(nan) == nan
  
      assert erf(oo) == 1
      assert erf(-oo) == -1
  
      assert erf(0) == 0
  
      assert erf(-2) == -erf(2)
      assert erf(-x*y) == -erf(x*y)
      assert erf(-x - y) == -erf(x + y)
  
  def test_erf_series():
      assert erf(x).series(x, 0, 7) == 2*x/sqrt(pi) - \
          2*x**3/3/sqrt(pi) + x**5/5/sqrt(pi) + O(x**7)
  
  def test_erf_evalf():
      assert abs( erf(Float(2.0)) - 0.995322265 )  <  1E-8  # XXX
  