FIX: Broken reviewable filter (#318)

plugin.rb

@@ -661,7 +661,7 @@ after_initialize do
         results.joins(<<~SQL
           INNER JOIN posts p ON p.id = target_id
           INNER JOIN topics t ON t.id = p.topic_id
-          INNER JOIN assignments a ON a.topic_id = t.id AND a.assigned_to_type == 'User'
+          INNER JOIN assignments a ON a.topic_id = t.id AND a.assigned_to_type = 'User'
           INNER JOIN users u ON u.id = a.assigned_to_id
         SQL
         )

spec/models/reviewable_spec.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+describe Reviewable do
+  fab!(:user) { Fabricate(:user) }
+  fab!(:admin) { Fabricate(:admin) }
+  fab!(:post1) { Fabricate(:post) }
+  fab!(:post2) { Fabricate(:post) }
+  fab!(:reviewable1) { Fabricate(:reviewable_flagged_post, target: post1) }
+  fab!(:reviewable2) { Fabricate(:reviewable_flagged_post, target: post2) }
+
+  before do
+    SiteSetting.assign_enabled = true
+  end
+
+  it "can filter by assigned_to" do
+    Assignment.create!(target: post1, topic_id: post1.topic.id, assigned_by_user: user, assigned_to: user)
+    Assignment.create!(target: post2, topic_id: post2.topic.id, assigned_by_user: user, assigned_to: admin)
+
+    expect(Reviewable.list_for(admin, additional_filters: { assigned_to: user.username })).to eq([reviewable1])
+  end
+end