Add example of unit tests in rectangles

rectangles/src/main.rs

@@ -20,6 +20,23 @@ impl Rectangle {
     fn can_hold(&self, other: &Rectangle) -> bool {
         self.width > other.width && self.height > other.height
     }
+
+    // convenience function to show use of Result<T,E> in tests
+    fn return_result(&self, is_succes: bool) -> Result<(), ()> {
+        if is_succes {
+            Ok(())
+        } else {
+            Err(())
+        }
+    }
+
+    // convenience function to show panic used in tests
+    fn return_panic(&self, is_panic: bool) {
+       if is_panic {
+       	  panic!("HEEELP");
+       }
+    }
+
 }
 
 fn main() {
@@ -79,3 +96,83 @@ fn area_tuple(dimensions: (u32, u32)) -> u32 {
 fn area_struct(rect: &Rectangle) -> u32 {
     rect.width * rect.height
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn square() {
+        let sq = Rectangle::square(4);
+
+        assert_eq!(sq.width, sq.height);
+    }
+
+    #[test]
+    fn area() {
+        let width = 4;
+        let height = 5;
+        let rect = Rectangle::build_rectangle(width, height);
+
+        assert_eq!(rect.area(), width * height);
+    }
+
+    #[test]
+    fn larger_can_hold_smaller() {
+        let smaller = Rectangle::build_rectangle(3, 4);
+        let larger = Rectangle::build_rectangle(5, 6);
+
+        assert!(larger.can_hold(&smaller));
+    }
+
+    #[test]
+    fn smaller_cannot_hold_larger() {
+        let smaller = Rectangle::build_rectangle(3, 4);
+        let larger = Rectangle::build_rectangle(5, 6);
+
+        assert!(!smaller.can_hold(&larger));
+    }
+
+    #[test]
+    fn result_success() -> Result<(), ()> {
+        let rect = Rectangle::build_rectangle(3, 4);
+
+        rect.return_result(true)?;
+
+        Ok(())
+    }
+
+    #[test]
+    fn result_will_fail_with_result() -> Result<(), ()> {
+        let rect = Rectangle::build_rectangle(3, 4);
+
+        rect.return_result(false)?;
+
+        Ok(())
+    }
+
+    #[test]
+    #[should_panic(expected = "HEEELP")]
+    fn result_panic() {
+        let rect = Rectangle::build_rectangle(3, 4);
+
+        rect.return_panic(true);
+    }
+
+    #[test]
+    #[should_panic]
+    fn result_will_not_panic_and_fail() {
+        let rect = Rectangle::build_rectangle(3, 4);
+
+        rect.return_panic(false);
+    }
+
+    #[test]
+    #[should_panic(expected = "HEEEEEEEEEEEEEEEEEEEELP")]
+    fn result_will_panic_but_with_wrong_message_and_fail() {
+        let rect = Rectangle::build_rectangle(3, 4);
+
+        rect.return_panic(false);
+    }
+
+}