test: Ensure Xsave FAMWrapper can be used

Regression test for missing `Default` implementation which was causing
compile errors when downstream uses referred to `Xsave` structure.

Signed-off-by: Patrick Roy <roypat@amazon.co.uk>

Author: roypat

src/x86_64/fam_wrappers.rs

@@ -160,9 +160,11 @@ pub type Xsave = FamStructWrapper<kvm_xsave2>;
 
 #[cfg(test)]
 mod tests {
-    use super::{CpuId, MsrList, Msrs};
+    use super::{CpuId, MsrList, Msrs, Xsave};
     use x86_64::bindings::kvm_cpuid_entry2;
 
+    use vmm_sys_util::fam::FamStruct;
+
     #[test]
     fn test_cpuid_eq() {
         let entries = &[kvm_cpuid_entry2::default(); 2];
@@ -215,4 +217,11 @@ mod tests {
         wrapper2.as_mut_slice()[0] = 1;
         assert!(wrapper == wrapper2);
     }
+    #[test]
+    fn test_xsave() {
+        let wrapper = Xsave::new(1).unwrap();
+        assert_eq!(wrapper.as_slice().len(), 1);
+        assert_eq!(wrapper.as_fam_struct_ref().len(), 1);
+        assert_eq!(wrapper.as_fam_struct_ref().len, 1);
+    }
 }