Fix unmemoized method

Author: andersonkrs

app/models/solid_queue/queue.rb

@@ -41,7 +41,7 @@ def size
     end
 
     def latency
-      @latency = begin
+      @latency ||= begin
         now = Time.current
         oldest_enqueued_at = ReadyExecution.queued_as(name).minimum(:created_at) || now
 

test/unit/queue_test.rb

@@ -54,10 +54,20 @@ class QueueTest < ActiveSupport::TestCase
     assert_equal 0, @default_queue.latency
   end
 
+  test "returns memoized latency after the first call" do
+    travel_to 5.minutes.from_now
+
+    assert_in_delta 5.minutes.to_i, @background_queue.latency, 1.second.to_i
+
+    travel_to 10.minutes.from_now
+
+    assert_in_delta 5.minutes.to_i, latency, 1.second.to_i
+  end
+
   test "return human latency on each queue" do
     travel_to 5.minutes.from_now
 
-    assert_match /5 minutes/, @background_queue.human_latency
-    assert_match /0 seconds/, @default_queue.human_latency
+    assert_match (/5 minutes/), @background_queue.human_latency
+    assert_match (/0 seconds/), @default_queue.human_latency
   end
 end