add start line test for string conversion

src/start_line.rs

@@ -47,8 +47,15 @@ impl<'a> HTTPStartLine<'a> {
     }
 }
 
+impl<'a> Into<String> for HTTPStartLine<'a> {
+    fn into(self) -> String {
+        let version: String = self.version.into();
+        return format!("{} {} {}", self.method, self.target, version);
+    }
+}
+
 #[test]
-fn test_start_line() {
+fn test_parse() {
     struct Expect<'a> {
         method: &'a str,
         target: &'a str,
@@ -89,3 +96,9 @@ fn test_start_line() {
         }
     }
 }
+
+#[test]
+fn test_into_string() {
+    let sl: String = HTTPStartLine::new("POST", "/health", HTTPVersion::Http2).into();
+    assert_eq!("POST /health HTTP/2".to_string(), sl);
+}