Add generated snapshots

tests/snapshots/output/numbers.snapshot.txt

@@ -0,0 +1,21 @@
+   1 struct Rectangle {
+   2     width: u32,
+   3     height: u32,
+   4 }
+   5 
+   6 fn main() {
+   7     let rect1 = Rectangle { width: 30, height: 50 };
+   8 
+   9     println!(
+  10         "The perimeter of the rectangle is {} pixels.",
+  11         perimeter(&rect1)
+  12     );
+  13 }
+  14 
+  15 fn area(rectangle: &Rectangle) -> u32 {
+  16     rectangle.width * rectangle.height
+  17 }
+  18 
+  19 fn perimeter(rectangle: &Rectangle) -> u32 {
+  20     (rectangle.width + rectangle.height) * 2
+  21 }