Warn if with_them is used before where is defined

Author: splattael

lib/rspec/parameterized/core.rb

@@ -79,6 +79,9 @@ def with_them(*args, &b)
           @parameter ||= nil
 
           if @parameter.nil?
+            format = ->(b) { b.source_location&.join(':') || '?' }
+            warn "#{format[b]}: `where` not defined."
+
             @parameterized_pending_cases ||= []
             @parameterized_pending_cases << [args, b]
           else