Dealing with piecewise equations returned by sympy integrate

In sympy I have an integral which returns a Piecewise object, e.g.

In [2]: from sympy.abc import x,y,z

In [3]: test = exp(-x**2/z**2)

In [4]: itest = integrate(test,(x,0,oo))

In [5]: itest
Out[5]: 
⎧   ___                                                   
⎪ ╲╱ π ⋅z       │                 ⎛      1          ⎞│   π
⎪ ───────   for │periodic_argument⎜──────────────, ∞⎟│ ≤ ─
⎪    2          │                 ⎜          2      ⎟│   2
⎪               │                 ⎝polar_lift (z)   ⎠│    
⎪                                                         
⎪∞                                                        
⎪⌠                                                        
⎨⎮    2                                                   
⎪⎮  -x                                                    
⎪⎮  ───                                                   
⎪⎮    2                                                   
⎪⎮   z                                                    
⎪⎮ ℯ    dx                    otherwise                   
⎪⌡                                                        
⎪0                                                        
⎩    

I would like to extract just the first branch of this piecewise equation, in other words, I would like to be able to do something like itest.parts(0)to extract simply sqrt(pi)*z/2. I can't seem to find any way to do this, but perhaps I am using the wrong search terms in the documentation. Any ideas?

Edit

Poking around a bit, I've managed to find that if I do itest.args[0][0] I can extract this expression. This seems like a bit of a hack, however. Is there a better approach?