Update Exercises Directory Names to Reflect Order

exercises/15_traits/traits1.rs

@@ -0,0 +1,42 @@
+// traits1.rs
+//
+// Time to implement some traits! Your task is to implement the trait
+// `AppendBar` for the type `String`. The trait AppendBar has only one function,
+// which appends "Bar" to any object implementing this trait.
+//
+// Execute `rustlings hint traits1` or use the `hint` watch subcommand for a
+// hint.
+
+// I AM NOT DONE
+
+trait AppendBar {
+    fn append_bar(self) -> Self;
+}
+
+impl AppendBar for String {
+    // TODO: Implement `AppendBar` for type `String`.
+}
+
+fn main() {
+    let s = String::from("Foo");
+    let s = s.append_bar();
+    println!("s: {}", s);
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn is_foo_bar() {
+        assert_eq!(String::from("Foo").append_bar(), String::from("FooBar"));
+    }
+
+    #[test]
+    fn is_bar_bar() {
+        assert_eq!(
+            String::from("").append_bar().append_bar(),
+            String::from("BarBar")
+        );
+    }
+}