diff --git a/src/robot.rs b/src/robot.rs
index a06e218..7ab8c5a 100644
--- a/src/robot.rs
+++ b/src/robot.rs
@@ -56,6 +56,19 @@ pub struct Position {
     pub y: i32,
 }
 
+/// Check if instructions list is valid.
+pub fn is_instructions(v: &Vec<char>) -> bool {
+    for c in v {
+        match c {
+            'F' => continue,
+            'R' => continue,
+            'L' => continue,
+            _ => return false,
+        }
+    }
+    true
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -95,4 +108,17 @@ mod tests {
         assert_eq!(r.p.x, 0);
         assert_eq!(r.p.y, 3);
     }
+
+    #[test]
+    fn is_instructions_test() {
+        let v = vec!['F', 'R', 'L', 'F'];
+        assert!(is_instructions(&v));
+    }
+
+    #[test]
+    #[should_panic]
+    fn is_instructions_test_fail() {
+        let v = vec!['F', 'R', 'L', 'Z'];
+        assert!(is_instructions(&v));
+    }
 }
diff --git a/src/world.rs b/src/world.rs
index 927a82a..357b82d 100644
--- a/src/world.rs
+++ b/src/world.rs
@@ -3,31 +3,3 @@ pub struct World {
     pub x: i32,
     pub y: i32,
 }
-
-pub fn is_instructions(v: &Vec<char>) -> bool {
-    for c in v {
-        match c {
-            'F' => continue,
-            'R' => continue,
-            'L' => continue,
-            _ => return false,
-        }
-    }
-    true
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    #[test]
-    fn is_instructions_test() {
-        let v = vec!['F', 'R', 'L', 'F'];
-        assert!(is_instructions(&v));
-    }
-    #[test]
-    #[should_panic]
-    fn is_instructions_test_fail() {
-        let v = vec!['F', 'R', 'L', 'Z'];
-        assert!(is_instructions(&v));
-    }
-}