Adds test for simple case of string replacement

+ rustfmt

src/lib/builtins/string.rs

@@ -742,11 +742,12 @@ pub fn replace(this: &Value, args: &[Value], ctx: &mut Interpreter) -> ResultVal
     let replacement_str: &str = &ctx.value_to_rust_string(&args[1]);
     // The Rust pattern is interpreted as a Regex and replaced in the original string with
     // the replacement by using Regex.replace_all
-    let result_str = Regex::new(pattern_str).unwrap().replace_all(this_str, replacement_str);
+    let result_str = Regex::new(pattern_str)
+        .unwrap()
+        .replace_all(this_str, replacement_str);
     Ok(to_value(result_str.into_owned()))
 }
 
-
 /// Create a new `String` object
 pub fn create_constructor(global: &Value) -> Value {
     // Create constructor function object
@@ -1061,4 +1062,17 @@ mod tests {
         );
         assert_eq!(forward(&mut engine, "result4[0]"), "B");
     }
+
+    #[test]
+    fn replace() {
+        let realm = Realm::create();
+        let mut engine = Executor::new(realm);
+        let init = r#"
+        var str = 'The quick brown fox jumps over the lazy dog. If the dog reacted, was it really lazy?';
+        var result = str.replace('dog', 'monkey');
+        "#;
+
+        forward(&mut engine, init);
+        assert_eq!(forward(&mut engine, "result"), "The quick brown fox jumps over the lazy monkey. If the monkey reacted, was it really lazy?");
+    }
 }