audit: prefer assert/refute_predicate over File.exist?

Library/Homebrew/dev-cmd/audit.rb

@@ -967,6 +967,14 @@ class FormulaAuditor
       problem "Use `assert_match` instead of `assert ...include?`"
     end
 
+    if line =~ /(assert File\.exist\?|File\.exist\?)/
+      problem "Use `assert_predicate <path_to_file>, :exist?` instead of `#{Regexp.last_match(1)}`"
+    end
+
+    if line =~ /(assert !File\.exist\?|!File\.exist\?)/
+      problem "Use `refute_predicate <path_to_file>, :exist?` instead of `#{Regexp.last_match(1)}`"
+    end
+
     return unless @strict
 
     problem "`#{Regexp.last_match(1)}` in formulae is deprecated" if line =~ /(env :(std|userpaths))/