Reduce nesting of macrotest test cases

test_suite/tests/expand/default_ty_param.rs

@@ -0,0 +1,14 @@
+use serde::{Serialize, Deserialize};
+
+trait AssociatedType {
+    type X;
+}
+
+impl AssociatedType for i32 {
+    type X = i32;
+}
+
+#[derive(Serialize, Deserialize)]
+struct DefaultTyParam<T: AssociatedType<X = i32> = i32> {
+    phantom: PhantomData<T>,
+}