Complete tests section

exercises/tests/tests1.rs

@@ -10,7 +10,7 @@
 mod tests {
     #[test]
     fn you_can_assert() {
-        assert!();
+        assert!(true);
     }
 }
 

exercises/tests/tests2.rs

@@ -6,7 +6,7 @@
 mod tests {
     #[test]
     fn you_can_assert_eq() {
-        assert_eq!();
+        assert_eq!(true, true);
     }
 }
 

exercises/tests/tests3.rs

@@ -13,7 +13,11 @@ mod tests {
 
     #[test]
     fn is_true_when_even() {
-        assert!();
+        assert!(is_even(42));
+    }
+
+    fn is_false_when_odd() {
+        assert!(!is_even(69));
     }
 }