Warn if where if was redefined

Author: splattael

lib/rspec/parameterized/core.rb

@@ -39,6 +39,10 @@ def initialize(arg_names, &block)
         #     end
         #
         def where(*args, &b)
+          if @parameter
+            format = ->(b) { b.source_location&.join(':') || '?' }
+            warn "#{format[b]}: `where` redefined. Discarding old definition at #{format[@parameter.block]}."
+          end
 
           if args.size == 1 && args[0].instance_of?(Hash)
             naming_func = args.first.delete(:case_names)