Drop unused import

I expect that we will not want to retain the original copy of a Card
after merging, cutting, rotating, etc. This function signature says that
the value moves into the method and goes away. If this becomes an
annoyance, then we change it.

src/card.rs

@@ -1,10 +1,8 @@
 //! TODO: module doc :v
 
-use std::ops::Deref;
-
 /// Value for the "sub tiles" inside a room tile
 #[derive(Clone, Copy, Debug, Default, PartialEq)]
-enum Cell {
+pub enum Cell {
   #[default]
   Empty,
   NW,
@@ -15,7 +13,7 @@ enum Cell {
 }
 
 #[derive(Clone, Copy, Debug)]
-enum CutLine {
+pub enum CutLine {
   VertLeft,
   VertRight,
   HorizUpper,
@@ -23,26 +21,26 @@ enum CutLine {
 }
 
 #[derive(Clone, Copy, Debug)]
-enum FlipDir {
+pub enum FlipDir {
   Vertical,
   Horizontal,
 }
 
 #[derive(Clone, Copy, Debug)]
-enum TransposeIndex {
+pub enum TransposeIndex {
   First,
   Second,
   Third,
 }
 
 #[derive(Clone, Copy, Debug)]
-enum TransposeSelection {
+pub enum TransposeSelection {
   Column(TransposeIndex),
   Row(TransposeIndex),
 }
 
 #[derive(Clone, Copy, Debug)]
-enum RotationDir {
+pub enum RotationDir {
   Clockwise,
   CounterClockwise,
 }
@@ -50,7 +48,7 @@ enum RotationDir {
 /// An invidiual room, or "card" in the player's hand. The room may
 /// *or may not* be valid, yet.
 #[derive(Clone, Copy, Debug, Default, PartialEq)]
-struct Card {
+pub struct Card {
   cells: [Cell; 9],
   nw: bool,
   n: bool,
@@ -115,19 +113,19 @@ impl Card {
   }
 
   /// Cuts this Card on the given line. Returns two cards
-  pub fn cut(&self, line: CutLine) -> (Self, Self) {
+  pub fn cut(self, line: CutLine) -> (Self, Self) {
     todo!();
   }
 
-  pub fn flip(&self, flip: FlipDir) -> (Self) {
+  pub fn flip(self, flip: FlipDir) -> Self {
     todo!();
   }
 
-  pub fn transpose(&self, other: &Self, selection: TransposeSelection) -> (Self, Self) {
+  pub fn transpose(self, other: Self, selection: TransposeSelection) -> (Self, Self) {
     todo!();
   }
 
-  pub fn rotate(&self, dir: RotationDir) {
+  pub fn rotate(self, dir: RotationDir) {
     todo!();
   }
 }
@@ -191,6 +189,60 @@ mod test {
     assert!(extra_doors.is_none());
   }
 
+  #[test]
+  fn check_merge_doors() {
+    let bottom = Card {
+      cells: NW_TRIANGLE,
+      s: true,  // Test that this is not overwritten by an empty tile
+      se: true, // Test that this is subsumed by another door
+      e: true,  // Test that this is popped off into the second card
+      ..Default::default()
+    };
+
+    let top = Card {
+      cells: [
+        Cell::Empty,
+        Cell::Empty,
+        Cell::Empty,
+        Cell::Empty,
+        Cell::Empty,
+        Cell::Filled,
+        Cell::Empty,
+        Cell::Empty,
+        Cell::Filled,
+      ],
+      se: true, // Test that this is subsumed by another door
+      n: true,  // Test that is is dropped because no floor
+      ..Default::default()
+    };
+
+    let expected = Card {
+      cells: [
+        Cell::Empty,
+        Cell::Empty,
+        Cell::NW,
+        Cell::Empty,
+        Cell::NW,
+        Cell::Filled,
+        Cell::NW,
+        Cell::Filled,
+        Cell::Filled,
+      ],
+      s: true,
+      se: true,
+      ..Default::default()
+    };
+
+    let expected_doors = Card {
+      e: true,
+      ..Default::default()
+    };
+
+    let (stacked, extra_doors) = bottom.merge(top);
+    assert_eq!(stacked, expected);
+    assert_eq!(extra_doors, Some(expected_doors));
+  }
+
   /// Merging two triangular [`Cell`]s should prefer the top-most one, *unless*
   /// they are opposites. See test [`merge_opposite_triangles()`].
   #[test]