Format y2015d15 and add check to prevent overriding days...

y2015/src/days/d15.rs

@@ -185,10 +185,4 @@ Cinnamon: capacity 2, durability 3, flavor -2, texture -1, calories 3";
         let result = process_part1(INPUT);
         assert_eq!(result, 62842880);
     }
-
-    #[test]
-    fn part2() {
-        let result = process_part2(INPUT);
-        assert_eq!(result, 0);
-    }
 }

y2015/src/days/d18.rs

@@ -0,0 +1,26 @@
+pub fn process_part1(input: &str) -> i32 {
+    0
+}
+
+pub fn process_part2(input: &str) -> i32 {
+    0
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const INPUT: &str = "{{EXAMPLE}}";
+
+    #[test]
+    fn part1() {
+        let result = process_part1(INPUT);
+        assert_eq!(result, 0);
+    }
+
+    #[test]
+    fn part2() {
+        let result = process_part2(INPUT);
+        assert_eq!(result, 0);
+    }
+}

y2015/src/days/mod.rs

@@ -17,3 +17,9 @@ pub mod d9;
 pub mod d16;
 
 pub mod d17;
+
+pub mod d18;
+
+pub mod d18;
+
+pub mod d18;