Restrict syntax for setting ink! e2e test node to auto (#2146)

* Restrict syntax for setting ink! e2e test node to auto

* Add changelog entry

---------

Co-authored-by: Michael Müller <michi@parity.io>

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Changed
 - Use name-only syntax for `anonymous` ink! event item configuration argument - [#2140](https://github.com/paritytech/ink/pull/2140)
 - Restrict syntax for setting default ink! e2e test runtime-only emulator - [#2143](https://github.com/paritytech/ink/pull/2143)
+- Restrict syntax for setting ink! e2e test node to auto - [#2146](https://github.com/paritytech/ink/pull/2146)
 - Bump Substrate crates - [#2141](https://github.com/paritytech/ink/pull/2141)
 - Minor fixes - [#2144](https://github.com/paritytech/ink/pull/2144),
 [#2137](https://github.com/paritytech/ink/pull/2137), [#2132](https://github.com/paritytech/ink/pull/2132)

crates/e2e/macro/src/config.rs

@@ -40,6 +40,7 @@ impl Default for Backend {
 pub enum Node {
     /// A fresh node instance will be spawned for the lifetime of the test.
     #[darling(word)]
+    #[darling(skip)]
     Auto,
     /// The test will run against an already running node at the supplied URL.
     Url(String),
@@ -137,7 +138,7 @@ mod tests {
 
     #[test]
     #[should_panic(expected = "ErrorUnknownField")]
-    fn config_works_backend_runtime_only_default_not_allowed() {
+    fn config_backend_runtime_only_default_not_allowed() {
         let input = quote! {
             backend(runtime_only(default)),
         };
@@ -164,23 +165,14 @@ mod tests {
     }
 
     #[test]
-    fn config_works_backend_node_default_auto() {
+    fn config_works_backend_node() {
         let input = quote! {
             backend(node),
         };
         let config =
             E2EConfig::from_list(&NestedMeta::parse_meta_list(input).unwrap()).unwrap();
 
         assert_eq!(config.backend(), Backend::Node(Node::Auto));
-    }
-
-    #[test]
-    fn config_works_backend_node_auto() {
-        let input = quote! {
-            backend(node(auto)),
-        };
-        let config =
-            E2EConfig::from_list(&NestedMeta::parse_meta_list(input).unwrap()).unwrap();
 
         match config.backend() {
             Backend::Node(node_config) => {
@@ -204,6 +196,18 @@ mod tests {
         }
     }
 
+    #[test]
+    #[should_panic(expected = "ErrorUnknownField")]
+    fn config_backend_node_auto_not_allowed() {
+        let input = quote! {
+            backend(node(auto)),
+        };
+        let config =
+            E2EConfig::from_list(&NestedMeta::parse_meta_list(input).unwrap()).unwrap();
+
+        assert_eq!(config.backend(), Backend::Node(Node::Auto));
+    }
+
     #[test]
     fn config_works_backend_node_url() {
         let input = quote! {