describe 'Timecop' do
  let(:time_1) { Time.local(2015, 12, 1) }
  let(:time_2) { Time.local(2016, 1, 21) }

  it 'travel in time' do
    Timecop.travel(time_1)

    expect(Time.now.year).to eq 2015
    expect(Time.now.month).to eq 12
    expect(Time.now.day).to eq 1

    Timecop.travel(time_2)

    expect(Time.now.year).to eq 2016
    expect(Time.now.month).to eq 1
    expect(Time.now.day).to eq 21

    Timecop.return
  end

  it 'when stub Time' do
    allow(Time).to receive(:now).and_return(time_1)

    expect(Time.now).to eq time_1

    allow(Time).to receive(:now).and_return(time_2)

    expect(Time.now).to eq time_2
  end
end

describe 'Timecop' do
  let(:time_1) { Time.local(2015, 12, 1) }
  let(:time_2) { Time.local(2016, 1, 21) }

  it 'travel in time' do
    Timecop.travel(time_1)

    expect(Time.now.year).to eq 2015
    expect(Time.now.month).to eq 12
    expect(Time.now.day).to eq 1

    Timecop.travel(time_2)

    expect(Time.now.year).to eq 2016
    expect(Time.now.month).to eq 1
    expect(Time.now.day).to eq 21

    Timecop.return
  end
end

--- 
+++ 
@@ -17,4 +17,14 @@
 
     Timecop.return
   end
+
+  it 'when stub Time' do
+    allow(Time).to receive(:now).and_return(time_1)
+
+    expect(Time.now).to eq time_1
+
+    allow(Time).to receive(:now).and_return(time_2)
+
+    expect(Time.now).to eq time_2
+  end
 end
Add tests to see how knapsack_pro handle case then someone stub Time.now
