Use RSpec's when_first_matching_example_defined if available (#1496)

This RSpec method was added in v3.5.0 to with expensive setup logic. It
results in similar behavior as just using `before(:example, ...)`, but
it will only run once instead of for each example.

Co-authored-by: Justin Gordon <justin@shakacode.com>

CHANGELOG.md

@@ -34,6 +34,8 @@ Changes since last non-beta release.
 
 ### Added
 - Exposed `reactHydrateOrRender` utility via [PR 1481](https://github.com/shakacode/react_on_rails/pull/1481) by [vaukalak](https://github.com/vaukalak).
+- Optimized `ReactOnRails::TestHelper`'s RSpec integration using
+  `when_first_matching_example_defined` via [PR 1496](https://github.com/shakacode/react_on_rails/pull/1496)
 
 ### [13.1.0] - 2022-08-20
 

lib/react_on_rails/test_helper.rb

@@ -35,8 +35,17 @@ module TestHelper
     def self.configure_rspec_to_compile_assets(config, *metatags)
       metatags = %i[js server_rendering controller] if metatags.empty?
 
+      # Supported since RSpec 3.5.0
+      supports_first_matching_example = config.respond_to?(:when_first_matching_example_defined)
+
       metatags.each do |metatag|
-        config.before(:example, metatag) { ReactOnRails::TestHelper.ensure_assets_compiled }
+        if supports_first_matching_example
+          config.when_first_matching_example_defined(metatag) do
+            ReactOnRails::TestHelper.ensure_assets_compiled
+          end
+        else
+          config.before(:example, metatag) { ReactOnRails::TestHelper.ensure_assets_compiled }
+        end
       end
     end