FEATURE: allow user search API to restrict to group

spec/models/user_search_spec.rb

@@ -43,6 +43,16 @@ describe UserSearch do
     expect(search_for("under_").length).to eq(1)
   end
 
+  it 'allows filtering by group' do
+    group = Fabricate(:group)
+    sam = Fabricate(:user, username: 'sam')
+    _samantha = Fabricate(:user, username: 'samantha')
+    group.add(sam)
+
+    results = search_for("sam", group: group)
+    expect(results.count).to eq(1)
+  end
+
   # this is a seriously expensive integration test,
   # re-creating this entire test db is too expensive reuse
   it "operates correctly" do