test(term): add test to direction

Cargo.toml

@@ -36,6 +36,7 @@ jsonwebtoken       = { version = "9.3.0" }
 kvsd               = { version = "0.1.3", default-features = false }
 moka               = { version = "0.12.7", features = ["future"] }
 parse_duration     = { version = "2.1.1" }
+proptest           = { version = "1.4.0" }
 rand               = { version = "0.8.5" }
 reqwest            = { version = "0.11.24", default-features = false, features = ["rustls-tls", "json"] }
 serde              = { version = "1", features = ["derive"] }

crates/synd_term/Cargo.toml

@@ -68,6 +68,7 @@ axum-server  = { workspace = true }
 fake         = { workspace = true }
 insta        = { workspace = true }
 kvsd         = { workspace = true }
+proptest     = { workspace = true }
 serial_test  = { version = "3.1.1", default_features = false, features = ["async", "file_locks"] }
 tempfile     = { workspace = true }
 tokio-stream = "0.1.15"

crates/synd_term/proptest-regressions/application/direction.txt

@@ -0,0 +1,7 @@
+# Seeds for failure cases proptest has generated in the past. It is
+# automatically read and these particular cases re-run before any
+# novel cases are generated.
+#
+# It is recommended to check this file in to source control so that
+# everyone who runs the test benefits from these saved cases.
+cc 41acc663e9b0dfdd2bb6fbc916e18a1842a5821e4857e4e440d48899199d5719 # shrinks to dir = Up, index = 1, len = 0, out = Wrapping

crates/synd_term/src/application/direction.rs

@@ -6,7 +6,7 @@ pub(crate) enum Direction {
     Right,
 }
 
-#[derive(PartialEq, Eq, Clone, Copy)]
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
 pub(crate) enum IndexOutOfRange {
     Wrapping,
     #[allow(dead_code)]
@@ -21,7 +21,7 @@ impl Direction {
     )]
     pub(crate) fn apply(self, index: usize, len: usize, out: IndexOutOfRange) -> usize {
         if len == 0 {
-            return index;
+            return 0;
         }
         let diff = match self {
             Direction::Up | Direction::Left => -1,
@@ -44,3 +44,47 @@ impl Direction {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use proptest::prelude::{prop_oneof, proptest, Just, ProptestConfig, Strategy};
+
+    proptest! {
+        #![proptest_config(ProptestConfig::default())]
+        #[test]
+        #[allow(clippy::cast_possible_wrap)]
+        fn apply(
+            dir in direction_strategy(),
+            index in 0..10_usize,
+            len in 0..10_usize,
+            out in index_out_of_range_strategy())
+        {
+            let apply = dir.apply(index, len,out) as i64;
+            let index = index as i64;
+            let len = len as i64;
+            assert!(
+                (apply - index).abs() == 1 ||
+                apply == 0 ||
+                apply == len-1
+            );
+        }
+
+
+    }
+    fn direction_strategy() -> impl Strategy<Value = Direction> {
+        prop_oneof![
+            Just(Direction::Up),
+            Just(Direction::Down),
+            Just(Direction::Left),
+            Just(Direction::Right),