Append generated test macro so next test macros are aware of it

`#[gtest]` will benefit from la10736/rstest#291, we could also benefit
other test macros.

It is an attempt to improve capabilities among test macros to avoid
duplicated test runs which is rare to be aware of.

The rationale is simple: procedure of attribute macro see only
attributes following it. Macros next to processing macro will not see
generated macro if it is generated in-place. So, instead of generating
test macro in-place, appending generated test macro will let macros next
to processing macro have chance to react, for example, not generate test
macro if there is already one.

We could deprecate `#[googletest::test]` oneday after la10736/rstest#291
released.

See: tokio-rs/tokio#6497, d-e-s-o/test-log#46, frondeus/test-case#143,
la10736/rstest#291, kezhuw/stuck#53.
Refs: rust-lang/rust#67839, rust-lang/rust#82419.

googletest_macro/src/lib.rs

@@ -14,8 +14,8 @@
 
 use quote::quote;
 use syn::{
-    parse_macro_input, punctuated::Punctuated, spanned::Spanned, Attribute, DeriveInput, FnArg,
-    ItemFn, PatType, ReturnType, Signature, Type,
+    parse_macro_input, parse_quote, punctuated::Punctuated, spanned::Spanned, Attribute,
+    DeriveInput, FnArg, ItemFn, PatType, ReturnType, Signature, Type,
 };
 
 /// Marks a test to be run by the Google Rust test runner.
@@ -75,7 +75,7 @@ pub fn gtest(
     _args: proc_macro::TokenStream,
     input: proc_macro::TokenStream,
 ) -> proc_macro::TokenStream {
-    let ItemFn { attrs, sig, block, .. } = parse_macro_input!(input as ItemFn);
+    let ItemFn { mut attrs, sig, block, .. } = parse_macro_input!(input as ItemFn);
     let (outer_return_type, trailer) = if attrs
         .iter()
         .any(|attr| attr.path().is_ident("should_panic"))
@@ -164,6 +164,13 @@ pub fn gtest(
                 )
             }
         };
+
+    if !attrs.iter().any(is_test_attribute) && !is_rstest_enabled {
+        let test_attr: Attribute = parse_quote! {
+            #[::core::prelude::v1::test]
+        };
+        attrs.push(test_attr);
+    };
     let function = quote! {
         #(#attrs)*
         #outer_sig -> #outer_return_type {
@@ -175,16 +182,7 @@ pub fn gtest(
             #trailer
         }
     };
-
-    let output = if attrs.iter().any(is_test_attribute) || is_rstest_enabled {
-        function
-    } else {
-        quote! {
-            #[::core::prelude::v1::test]
-            #function
-        }
-    };
-    output.into()
+    function.into()
 }
 
 /// Alias for [`googletest::gtest`].