Add test coverage for the StatusCode is_xxxxx() functions (#545)

tests/status_code.rs

@@ -31,3 +31,52 @@ fn roundtrip() {
         assert_eq!(sstr, status.as_str());
     }
 }
+
+#[test]
+fn is_informational() {
+    assert!(status_code(100).is_informational());
+    assert!(status_code(199).is_informational());
+
+    assert!(!status_code(200).is_informational());
+}
+
+#[test]
+fn is_success() {
+    assert!(status_code(200).is_success());
+    assert!(status_code(299).is_success());
+
+    assert!(!status_code(199).is_success());
+    assert!(!status_code(300).is_success());
+}
+
+#[test]
+fn is_redirection() {
+    assert!(status_code(300).is_redirection());
+    assert!(status_code(399).is_redirection());
+
+    assert!(!status_code(299).is_redirection());
+    assert!(!status_code(400).is_redirection());
+}
+
+#[test]
+fn is_client_error() {
+    assert!(status_code(400).is_client_error());
+    assert!(status_code(499).is_client_error());
+
+    assert!(!status_code(399).is_client_error());
+    assert!(!status_code(500).is_client_error());
+}
+
+#[test]
+fn is_server_error() {
+    assert!(status_code(500).is_server_error());
+    assert!(status_code(599).is_server_error());
+
+    assert!(!status_code(499).is_server_error());
+    assert!(!status_code(600).is_server_error());
+}
+
+/// Helper method for readability
+fn status_code(status_code: u16) -> StatusCode {
+    StatusCode::from_u16(status_code).unwrap()
+}