Fix r2r2r_identity test

Reusing a plan for different arrays than it was created with requires that they
have the same size and alignment as was used for creating the plan. By
assigning an entirely new vec to `a` - which may have a different alignment -
this test currently violating that requirement.

Fix this by filling the existing vec instead of allocating a new one

Author: LingMan

fftw/tests/r2r.rs

@@ -25,7 +25,9 @@ fn r2r2r_identity() {
     let factor = 2. * n as f64;
 
     // Vector of ones.
-    a = vec![1.0f64; n];
+    for a_i in a.iter_mut() {
+        *a_i = 1.0;
+    }
 
     // Forward pass.
     fwd.r2r(&mut a, &mut b).unwrap();