add more proptests for output

output/src/direction.rs

@@ -0,0 +1,33 @@
+use crate::*;
+/// A cardinal direction.
+#[derive(Copy, Clone, PartialEq)]
+pub enum Direction { North, South, East, West, Above, Below }
+impl Direction {
+    pub fn split_fixed <N: Coordinate> (self, area: impl Area<N>, a: N) -> ([N;4],[N;4]) {
+        let [x, y, w, h] = area.xywh();
+        match self {
+            North => ([x, y.plus(h).minus(a), w, a], [x, y, w, h.minus(a)]),
+            South => ([x, y, w, a], [x, y.plus(a), w, h.minus(a)]),
+            East  => ([x, y, a, h], [x.plus(a), y, w.minus(a), h]),
+            West  => ([x.plus(w).minus(a), y, a, h], [x, y, w.minus(a), h]),
+            Above | Below => (area.xywh(), area.xywh())
+        }
+    }
+}
+#[cfg(test)] mod test_op_transform {
+    use super::*;
+    use proptest::prelude::*;
+    proptest! {
+        #[test] fn test_direction (
+            x in u16::MIN..u16::MAX,
+            y in u16::MIN..u16::MAX,
+            w in u16::MIN..u16::MAX,
+            h in u16::MIN..u16::MAX,
+            a in u16::MIN..u16::MAX,
+        ) {
+            for d in [North, South, East, West, Above, Below].iter() {
+                let _ = d.split_fixed([x, y, w, h], a);
+            }
+        }
+    }
+}