Allow import of layout_test into 3rd party crates (#3463)

* Expose layout tests

Currently I can't import tests because `cfg(test)` isn't sent to sub-dependencies.   This allows you to set a `yew/test` and import into your own tests.

* Update Cargo.toml

* Update lib.rs

* Update lib.rs

* Update lib.rs

* AnyScope::test needs feature = test cfg + fmt

---------

Co-authored-by: Elina <imelina@elina.website>

packages/yew/Cargo.toml

@@ -96,6 +96,7 @@ ssr = ["dep:html-escape", "dep:base64ct", "dep:bincode"]
 csr = []
 hydration = ["csr", "dep:bincode"]
 default = []
+test = []
 
 [package.metadata.docs.rs]
 all-features = true

packages/yew/src/html/component/scope.rs

@@ -513,7 +513,7 @@ mod feat_csr {
     use crate::scheduler;
 
     impl AnyScope {
-        #[cfg(test)]
+        #[cfg(any(test, feature = "test"))]
         pub(crate) fn test() -> Self {
             Self {
                 type_id: TypeId::of::<()>(),

packages/yew/src/lib.rs

@@ -293,8 +293,7 @@ mod app_handle;
 #[cfg(feature = "csr")]
 mod renderer;
 
-#[cfg(feature = "csr")]
-#[cfg(test)]
+#[cfg(all(feature = "csr", any(test, feature = "test")))]
 #[allow(missing_docs)]
 pub mod tests;