#[derive(Debug)]
pub struct Rectangle {
    length: u32,
    width: u32
}

impl Rectangle {
    pub fn can_hold(&self, other: &Rectangle) -> bool {
        self.length > other.length && self.width > other.width
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn larger_can_hold_smaller() {
        let larger = Rectangle { length: 8, width: 8};
        let smaller = Rectangle { length:5, width: 5};

        assert!(larger.can_hold(&smaller));
    }
}

#[derive(Debug)]
pub struct Rectangle {
    length: u32,
    width: u32
}

impl Rectangle {
    pub fn can_hold(&self, other: &Rectangle) -> bool {
        self.length > other.length && self.width > other.width
    }
}

#[cfg(test)]
mod tests {
    #[test]
    fn it_works() {
    }

    #[test]
    fn it_panics() {
        panic!("Make this test fail!");
    }
}

--- 
+++ 
@@ -12,12 +12,13 @@
 
 #[cfg(test)]
 mod tests {
-    #[test]
-    fn it_works() {
-    }
+    use super::*;
 
     #[test]
-    fn it_panics() {
-        panic!("Make this test fail!");
+    fn larger_can_hold_smaller() {
+        let larger = Rectangle { length: 8, width: 8};
+        let smaller = Rectangle { length:5, width: 5};
+
+        assert!(larger.can_hold(&smaller));
     }
 }
Add test which uses assert!
