Specs / implementation for Throttler#when_does_next_period_start?

app/lib/throttler.rb

@@ -32,6 +32,10 @@ class Throttler
     @entries[unique_id] || 0
   end
 
+  def when_does_next_period_start?(now = Time.now)
+    Time.at(current_period * time_unit_in_seconds.to_i) + time_unit_in_seconds
+  end
+
 private
 
   def reset_everything(now)

spec/lib/throttler_spec.rb

@@ -1,11 +1,11 @@
 require "spec_helper"
 
 describe Throttler do
-  NOW = Time.new("2018-05-18T09:38:02.259-05:00")
+  let(:stub_time) { Time.new(2018, 5, 18, 9, 38, 2) }
 
   it "sets a time unit window size" do
     expected_time_period = 25246440
-    one_min              = Throttler.new(1.minute, NOW)
+    one_min              = Throttler.new(1.minute, stub_time)
 
     expect(one_min.current_period).to eq(expected_time_period)
     expect(one_min.time_unit_in_seconds).to eq(60)
@@ -13,23 +13,31 @@ describe Throttler do
   end
 
   it "increments the count" do
-    t   = Throttler.new(1.minute, NOW)
+    t   = Throttler.new(1.minute, stub_time)
     uid = 123
 
     # Ignore events from the past.
-    t.record_event(uid, NOW - 90)
+    t.record_event(uid, stub_time - 90)
     expect(t.usage_count_for(uid)).to eq(0)
 
     # Record events from the present
-    t.record_event(uid, NOW + 30)
+    t.record_event(uid, stub_time + 30)
     expect(t.usage_count_for(uid)).to eq(1)
 
     # Keep recording events from the present
-    t.record_event(uid, NOW + 31)
+    t.record_event(uid, stub_time + 31)
     expect(t.usage_count_for(uid)).to eq(2)
 
     # Invalidate cache when time window passes
-    t.record_event(uid, NOW + 75)
+    t.record_event(uid, stub_time + 75)
     expect(t.usage_count_for(uid)).to eq(0)
   end
+
+  it "tells you when the next time period starts" do
+    one_hour  = Throttler.new(1.hour, stub_time)
+    next_hour = one_hour.when_does_next_period_start?(stub_time)
+    expect(next_hour).to be_kind_of(Time)
+    expect(next_hour.hour).to be(stub_time.hour + 1)
+    expect(next_hour.min).to  be(0)
+  end
 end