Add unit tests card flipping in both directions

src/card.rs

@@ -302,6 +302,20 @@ pub const NW_TRIANGLE: [Cell; 9] = [
   Cell::NW, Cell::Filled, Cell::Filled,
 ];
 
+#[rustfmt::skip]
+pub const SW_TRIANGLE: [Cell; 9] = [
+  Cell::SW, Cell::Filled, Cell::Filled,
+  Cell::Empty, Cell::SW, Cell::Filled,
+  Cell::Empty, Cell::Empty, Cell::SW,
+];
+
+#[rustfmt::skip]
+pub const NE_TRIANGLE: [Cell; 9] = [
+  Cell::NE, Cell::Empty, Cell::Empty,
+  Cell::Filled, Cell::NE, Cell::Empty,
+  Cell::Filled, Cell::Filled, Cell::NE
+];
+
 #[rustfmt::skip]
 pub const OCTAGON: [Cell; 9] = [
   Cell::NW, Cell::Filled, Cell::NE,
@@ -573,12 +587,36 @@ mod test {
 
   #[test]
   fn flip_triangle_vertical() {
-    todo!();
+    let tri = Card {
+      cells: NW_TRIANGLE,
+      ..Default::default()
+    };
+
+    let expected = Card {
+      cells: SW_TRIANGLE,
+      ..Default::default()
+    };
+
+    let result = tri.flip(FlipDir::Vertical);
+
+    assert_eq!(result, expected);
   }
 
   #[test]
   fn flip_triangle_horizontal() {
-    todo!();
+    let tri = Card {
+      cells: NW_TRIANGLE,
+      ..Default::default()
+    };
+
+    let expected = Card {
+      cells: NE_TRIANGLE,
+      ..Default::default()
+    };
+
+    let result = tri.flip(FlipDir::Horizontal);
+
+    assert_eq!(result, expected);
   }
 
   #[test]