add basic unit test

src/engine.rs

@@ -1,7 +1,9 @@
 extern crate piston_window;
 
 use piston_window::*;
+use std::f64::consts;
 
+#[derive(PartialEq, Debug)]
 struct Position {
     x: f64,
     y: f64,
@@ -32,6 +34,10 @@ impl Engine {
         }
     }
 
+    fn closest_point(pos: Position, angle: f64) -> Position {
+        return Position {x: 2., y: 2.}
+    }
+
     pub fn render(&mut self, context: Context, graphics: &mut G2d) {
 
         clear([1.0; 4], graphics);
@@ -66,3 +72,16 @@ impl Engine {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn closest_point() {
+        let origin = super::Position { x: 2.2, y: 2.3 };
+        let angle = 0.;
+        let closest = Engine::closest_point(origin, angle);
+        assert_eq!(closest, super::Position { x: 3.0, y: 2.3 });
+    }
+}