Create tests for if1.rs

This provides standardize feedback if a solution is correct. Fixes #46.

if/if1.rs

@@ -1,4 +1,4 @@
-fn bigger(a: i32, b:i32) -> i32 {
+pub fn bigger(a: i32, b:i32) -> i32 {
     // Complete this function to return the bigger number!
     // Do not use:
     // - return
@@ -7,11 +7,20 @@ fn bigger(a: i32, b:i32) -> i32 {
     // Scroll down for hints.
 }
 
-fn main() {
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn ten_is_bigger_than_eight() {
         assert_eq!(10, bigger(10, 8));
-    assert_eq!(42, bigger(32, 42));
     }
 
+    #[test]
+    fn fortytwo_is_bigger_than_thirtytwo() {
+        assert_eq!(42, bigger(32, 42));
+    }
+}