main.rs: Add overflow check for u8::MAX

1 files changed, 37 insertions, 8 deletions

diff --git a/src/main/rust/main.rs b/src/main/rust/main.rs
index 5b13d2a..9248661 100644
--- a/src/main/rust/main.rs
+++ b/src/main/rust/main.rs
@@ -21,7 +21,8 @@ pub struct App {
 #[error("An overflow error occurred")]
 #[diagnostic()]
 pub struct OverflowError {
-    msg: String,
+    #[help]
+    _msg: String,
 }
 
 fn main() -> Result<()> {
@@ -71,7 +72,7 @@ impl App {
     fn decrement_counter(&mut self) -> Result<(), OverflowError> {
         if self.counter == 0 {
             Err(OverflowError {
-                msg: "Overflow error occurred!".into(),
+                _msg: "Cannot count below 0".into(),
             })
         } else {
             self.counter -= 1;
@@ -79,9 +80,15 @@ impl App {
         }
     }
 
-    fn increment_counter(&mut self) -> Result<()> {
-        self.counter += 1;
-        Ok(())
+    fn increment_counter(&mut self) -> Result<(), OverflowError> {
+        if self.counter == u8::MAX {
+            Err(OverflowError {
+                _msg: "Cannot count above u8::MAX".into(),
+            })
+        } else {
+            self.counter += 1;
+            Ok(())
+        }
     }
 }
 
@@ -175,12 +182,34 @@ mod tests {
             .downcast_ref::<OverflowError>()
             .expect("something bad occurred");
 
-        let expected_err_msg: String = "Overflow error occurred!".into();
-        assert_eq!(casted_val.msg, expected_err_msg);
+        let expected_err_msg: String = "Cannot count below 0".into();
+        assert_eq!(casted_val._msg, expected_err_msg);
+        assert_eq!(
+            *casted_val,
+            OverflowError {
+                _msg: expected_err_msg,
+            },
+        );
+    }
+
+    #[test]
+    fn handle_key_event_inc_error() {
+        let mut app = App::default();
+        app.counter = u8::MAX;
+        let res = app.handle_key_event(KeyCode::Right.into());
+
+        assert!(res.is_err());
+        let res_err = res.unwrap_err();
+        let casted_val = res_err
+            .downcast_ref::<OverflowError>()
+            .expect("something bad occurred");
+
+        let expected_err_msg: String = "Cannot count above u8::MAX".into();
+        assert_eq!(casted_val._msg, expected_err_msg);
         assert_eq!(
             *casted_val,
             OverflowError {
-                msg: expected_err_msg,
+                _msg: expected_err_msg,
             },
         );
     }