add validation to exclude_category_ids

lib/topic_query.rb

@@ -17,13 +17,14 @@ class TopicQuery
         Integer === x && x >= 0
       end
 
-      array_zero_or_more = lambda do |x|
-        Array === x && x.length > 0 && x.all? { |i| Integer === i && i >= 0 }
+      array_int = lambda do |x|
+        Array === x && x.length > 0 && x.all? { |i| Integer === i }
       end
 
       {
         max_posts: zero_or_more,
         min_posts: zero_or_more,
+        exclude_category_ids: array_int
       }
     end
   end

spec/requests/list_controller_spec.rb

@@ -22,6 +22,12 @@ RSpec.describe ListController do
 
       get "/latest?max_posts=bob"
       expect(response.status).to eq(400)
+
+      get "/latest?exclude_category_ids=bob"
+      expect(response.status).to eq(400)
+
+      get "/latest?exclude_category_ids[]=bob"
+      expect(response.status).to eq(400)
     end
 
     it "doesn't throw an error with page params as an array" do