added documentation for cfg_panic

Author: chiw-goog

src/attributes/testing.md

@@ -81,6 +81,50 @@ fn mytest() {
     assert_eq!(1, 2, "values don't match");
 }
 ```
+### Different panic strategies
+
+The `cfg_panic` feature makes it possible to exercise different lines of code depending on the panic strategy. 
+The possible value is either `unwind` or `abort`.
+The following is a playful example on choosing the right beverage. 
+
+```toml
+#![feature(cfg_panic)]
+
+#[cfg(panic = "unwind")]
+fn ah(){ println!("Spit it out!!!!");}
+
+#[cfg(not(panic="unwind"))]
+fn ah(){ println!("This is not your party. Run!!!!");}
+
+fn drink(beverage: &str){
+   if beverage == "lemonade"{ ah();}
+   else{println!("Some refreshing {} is all I need.", beverage);}
+}
+
+fn main(){
+   drink("water");
+   drink("lemonade");
+}
+```
+
+Here is the same example rewritten.
+```toml
+#![feature(cfg_panic)]
+
+fn drink(beverage: &str) {
+   // You shouldn't drink too much sugary beverages.
+   if beverage == "lemonade" {
+     if cfg!(panic="abort"){ println!("This is not your party. Run!!!!");}
+     else{ println!("Spit it out!!!!");}
+   }
+   else{ println!("Some refreshing {} is all I need.", beverage); }
+}
+
+fn main() {
+    drink("water");
+    drink("lemonade");
+}
+```
 
 [_MetaListNameValueStr_]: ../attributes.md#meta-item-attribute-syntax
 [_MetaNameValueStr_]: ../attributes.md#meta-item-attribute-syntax