stress test new fftn() call with real-valued input

stress.py

@@ -24,6 +24,11 @@ def test():
     a=np.random.rand(*shape)-0.5 + 1j*np.random.rand(*shape)-0.5j
     b=pypocketfft.ifftn(pypocketfft.fftn(a,axes=axes,nthreads=nthreads),axes=axes,inorm=2,nthreads=nthreads)
     err = _l2error(a,b)
+    if err > cmaxerr:
+        cmaxerr = err
+        print("cmaxerr:", cmaxerr, shape, axes)
+    b=pypocketfft.ifftn(pypocketfft.fftn(a.real,axes=axes,nthreads=nthreads),axes=axes,inorm=2,nthreads=nthreads)
+    err = _l2error(a.real,b)
     if err > cmaxerr:
         cmaxerr = err
         print("cmaxerr:", cmaxerr, shape, axes)