修复ch11-01-writing-tests章节中无意义测试

更新到 024ee9542d

listings/ch11-writing-automated-tests/no-listing-10-result-in-tests/src/lib.rs

@@ -1,11 +1,21 @@
+pub fn add(left: usize, right: usize) -> usize {
+    left + right
+}
+
 #[cfg(test)]
 mod tests {
+    use super::*;
+
+    // ANCHOR: here
     #[test]
     fn it_works() -> Result<(), String> {
-        if 2 + 2 == 4 {
+        let result = add(2, 2);
+
+        if result == 4 {
             Ok(())
         } else {
             Err(String::from("two plus two does not equal four"))
         }
     }
+    // ANCHOR_END: here
 }