test: add test case for TupleField

Author: Young-Flash

crates/ide-assists/src/handlers/extract_struct_from_enum_variant.rs

@@ -466,6 +466,21 @@ enum Foo {
     Bar(Bar),
     Nil,
 }
+"#,
+        );
+        check_assist(
+            extract_struct_from_enum_variant,
+            r#"
+enum Foo {
+    Nil(Box$0<Self>, Arc<Box<Self>>),
+}
+"#,
+            r#"
+struct Nil(Box<Foo>, Arc<Box<Foo>>);
+
+enum Foo {
+    Nil(Nil),
+}
 "#,
         );
     }