tests: show fs leak result

Closes Homebrew/homebrew#41956.

Signed-off-by: Xu Cheng <xucheng@me.com>

Library/Homebrew/cmd/tests.rb

@@ -9,6 +9,14 @@ module Homebrew
         system("bundle", "install", "--path", "vendor/bundle")
       system "bundle", "exec", "rake", "test"
       Homebrew.failed = !$?.success?
+      if (fs_leak_log = HOMEBREW_LIBRARY/"Homebrew/test/fs_leak_log").file?
+        fs_leak_log_content = fs_leak_log.read
+        unless fs_leak_log_content.empty?
+          opoo "File leak is detected"
+          puts fs_leak_log_content
+          Homebrew.failed = true
+        end
+      end
     end
   end
 end