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Tests

Topics

  • stubs
  • blocks
  • yield

Performance Monitor

This is (a stripped down version of) an actual useful concept: a function that runs a block of code and then tells you how long it took to run.

Tests

performance_monitor_spec.rb
require "performance_monitor"

require "time"  # loads up the Time.parse method -- do NOT create time.rb!

describe "Performance Monitor" do
  before do
    @eleven_am = Time.parse("2011-1-2 11:00:00")
  end

  it "takes about 0 seconds to run an empty block" do
    elapsed_time = measure do
    end
    elapsed_time.should be_within(0.1).of(0)
  end

  it "takes exactly 0 seconds to run an empty block (with stubs)" do
    Time.stub(:now) { @eleven_am }
    elapsed_time = measure do
    end
    elapsed_time.should == 0
  end

  it "takes about 1 second to run a block that sleeps for 1 second" do
    elapsed_time = measure do
      sleep 1
    end
    elapsed_time.should be_within(0.1).of(1)
  end

  it "takes exactly 1 second to run a block that sleeps for 1 second (with stubs)" do
    fake_time = @eleven_am
    Time.stub(:now) { fake_time }
    elapsed_time = measure do
      fake_time += 60  # adds one minute to fake_time
    end
    elapsed_time.should == 60
  end

  it "runs a block N times" do
    n = 0
    measure(4) do
      n += 1
    end
    n.should == 4
  end

  it "returns the average time, not the total time, when running multiple times" do
    run_times = [8,6,5,7]
    fake_time = @eleven_am
    Time.stub(:now) { fake_time }
    average_time = measure(4) do
      fake_time += run_times.pop
    end
    average_time.should == 6.5
  end

  it "returns the average time when running a random number of times for random lengths of time" do
    fake_time = @eleven_am
    Time.stub(:now) { fake_time }
    number_of_times = rand(10) + 2
    average_time = measure(number_of_times) do
      delay = rand(10)
      fake_time += delay
    end
    average_time.should == (fake_time - @eleven_am).to_f/number_of_times
  end

end
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