Clean up and unify exercises

exercises/18_iterators/iterators1.rs

@@ -1,24 +1,28 @@
-// iterators1.rs
-//
 // When performing operations on elements within a collection, iterators are
 // essential. This module helps you get familiar with the structure of using an
 // iterator and how to go through elements within an iterable collection.
 //
 // Make me compile by filling in the `???`s
-//
-// Execute `rustlings hint iterators1` or use the `hint` watch subcommand for a
-// hint.
 
-#[test]
 fn main() {
-    let my_fav_fruits = vec!["banana", "custard apple", "avocado", "peach", "raspberry"];
-
-    let mut my_iterable_fav_fruits = ???;   // TODO: Step 1
-
-    assert_eq!(my_iterable_fav_fruits.next(), Some(&"banana"));
-    assert_eq!(my_iterable_fav_fruits.next(), ???);     // TODO: Step 2
-    assert_eq!(my_iterable_fav_fruits.next(), Some(&"avocado"));
-    assert_eq!(my_iterable_fav_fruits.next(), ???);     // TODO: Step 3
-    assert_eq!(my_iterable_fav_fruits.next(), Some(&"raspberry"));
-    assert_eq!(my_iterable_fav_fruits.next(), ???);     // TODO: Step 4
+    // You can optionally experiment here.
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn iterators() {
+        let my_fav_fruits = vec!["banana", "custard apple", "avocado", "peach", "raspberry"];
+
+        let mut my_iterable_fav_fruits = ???;   // TODO: Step 1
+
+        assert_eq!(my_iterable_fav_fruits.next(), Some(&"banana"));
+        assert_eq!(my_iterable_fav_fruits.next(), ???);     // TODO: Step 2
+        assert_eq!(my_iterable_fav_fruits.next(), Some(&"avocado"));
+        assert_eq!(my_iterable_fav_fruits.next(), ???);     // TODO: Step 3
+        assert_eq!(my_iterable_fav_fruits.next(), Some(&"raspberry"));
+        assert_eq!(my_iterable_fav_fruits.next(), ???);     // TODO: Step 4
+    }
 }