DEV: correctly detect chromium on macos (#35441)

When Chrome isn't installed, running "bin/rails qunit:test" would fail
because it wouldn't be able to detect that Chromium was installed.

This fixed that and also pass the detected browser to testem

lib/chrome_installed_checker.rb

@@ -17,7 +17,8 @@ class ChromeInstalledChecker
 
   def self.run
     if RbConfig::CONFIG["host_os"][/darwin|mac os/]
-      binary = "/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome"
+      chrome_path = "/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome"
+      binary = chrome_path if File.exist?(chrome_path)
     elsif system("command -v google-chrome-stable >/dev/null;")
       binary = "google-chrome-stable"
     end
@@ -38,5 +39,8 @@ class ChromeInstalledChecker
     if Gem::Version.new(version_match[0]) < Gem::Version.new("59")
       raise ChromeVersionTooLow.new("Chrome 59 or higher is required")
     end
+
+    # Return browser name for testem launcher (case-sensitive)
+    binary.include?("chromium") ? "Chromium" : "Chrome"
   end
 end

lib/tasks/qunit.rake

@@ -5,11 +5,12 @@ task "qunit:test", %i[qunit_path filter] do |_, args|
   require "socket"
   require "chrome_installed_checker"
 
-  begin
-    ChromeInstalledChecker.run
-  rescue ChromeInstalledChecker::ChromeError => err
-    abort err.message
-  end
+  detected_browser =
+    begin
+      ChromeInstalledChecker.run
+    rescue ChromeInstalledChecker::ChromeError => err
+      abort err.message
+    end
 
   unless system("command -v pnpm >/dev/null;")
     abort "pnpm is not installed. See https://pnpm.io/installation"
@@ -99,7 +100,10 @@ task "qunit:test", %i[qunit_path filter] do |_, args|
     end
     puts "Rails server is warmed up"
 
-    env = { "UNICORN_PORT" => unicorn_port.to_s }
+    env = {
+      "UNICORN_PORT" => unicorn_port.to_s,
+      "TESTEM_DEFAULT_BROWSER" => ENV["TESTEM_DEFAULT_BROWSER"].presence || detected_browser,
+    }
     cmd = []
 
     parallel = ENV["QUNIT_PARALLEL"]