assert new line at end of ppm

canvas/src/lib.rs

@@ -154,4 +154,11 @@ mod tests {
         let four_to_seven = ppm.split("\n").skip(3).collect::<Vec<&str>>().join("\n");
         assert_eq!(line4_7, four_to_seven);
     }
+
+    #[test]
+    fn ends_with_newline() {
+        let c = Canvas::new(5, 3);
+        let mut ppm = c.to_ppm();
+        assert_eq!(Some('\n'), ppm.pop());
+    }
 }