add extra unit test

Author: SOF3

tests/derive_delegate.rs

@@ -0,0 +1,26 @@
+#[portrait::make]
+trait Foo {
+    fn new(arg1: i32, arg2: &str, arg3: &mut i64) -> Self;
+    fn print(&self);
+    fn clone(&self) -> Self;
+    #[portrait(derive_delegate(reduce = |a, b| a && b))]
+    fn eq(&self, other: &Self) -> bool;
+}
+
+#[portrait::fill(portrait::default)]
+impl Foo for i32 { }
+
+#[portrait::fill(portrait::default)]
+impl Foo for String {}
+
+#[portrait::derive(Foo with portrait::derive_delegate)]
+struct Fields {
+    a: i32,
+    b: String,
+}
+
+fn main() {
+    fn assert(_: impl Foo) {}
+
+    assert(Fields { a: 1, b: String::new() });
+}