Merge pull request #1068 from laserlemon/random-order-performance

Use Array#shuffle for random spec ordering

benchmarks/sort_by_v_shuffle.rb

@@ -0,0 +1,42 @@
+require "benchmark"
+
+# This benchmark demonstrates the speed of Array#shuffle versus sorting by
+# random numbers. This is in reference to ordering examples using the
+# --order=rand command line flag. Array#shuffle also respects seeded random via
+# Kernel.srand.
+
+LIST = (1..1_000).to_a.freeze
+
+Benchmark.bmbm do |x|
+  x.report("sort_by") do
+    1_000.times do
+      LIST.sort_by { Kernel.rand(LIST.size) }
+    end
+  end
+
+  x.report("shuffle") do
+    1_000.times do
+      LIST.shuffle
+    end
+  end
+end
+
+# Ruby 2.0
+#
+# 21x over 100 list elements:
+#
+#                 user     system      total        real
+#   sort_by   0.080000   0.000000   0.080000 (  0.074924)
+#   shuffle   0.000000   0.000000   0.000000 (  0.003535)
+#
+# 27x over 1,000 list elements:
+#
+#                 user     system      total        real
+#   sort_by   0.870000   0.000000   0.870000 (  0.874661)
+#   shuffle   0.030000   0.000000   0.030000 (  0.031949)
+#
+# 31x over 10,000 list elements:
+#
+#                 user     system      total        real
+#   sort_by  10.690000   0.010000  10.700000 ( 10.695433)
+#   shuffle   0.330000   0.010000   0.340000 (  0.342375)

lib/rspec/core/configuration.rb

@@ -894,7 +894,7 @@ def randomize?
       # @private
       RANDOM_ORDERING = lambda do |list|
         Kernel.srand RSpec.configuration.seed
-        ordering = list.sort_by { Kernel.rand(list.size) }
+        ordering = list.shuffle
         Kernel.srand # reset random generation
         ordering
       end

spec/rspec/core/configuration_spec.rb

@@ -1333,10 +1333,12 @@ def metadata_hash(*args)
       end
 
       it 'can set random ordering' do
-        config.force :seed => "rand:37"
+        config.force :order => "rand:37"
         RSpec.stub(:configuration => config)
         list = [1, 2, 3, 4].extend(Extensions::Ordered::Examples)
-        Kernel.should_receive(:rand).and_return(3, 1, 4, 2)
+        Kernel.should_receive(:srand).ordered.once.with(37)
+        list.should_receive(:shuffle).ordered.and_return([2, 4, 1, 3])
+        Kernel.should_receive(:srand).ordered.once.with(no_args)
         expect(list.ordered).to eq([2, 4, 1, 3])
       end
 
@@ -1377,6 +1379,23 @@ def metadata_hash(*args)
     end
 
     describe '#order=' do
+      context 'given "random"' do
+        before { config.order = 'random:123' }
+
+        it 'sets order to "random"' do
+          expect(config.order).to eq('random')
+        end
+
+        it 'sets up random ordering' do
+          RSpec.stub(:configuration => config)
+          list = [1, 2, 3, 4].extend(Extensions::Ordered::Examples)
+          Kernel.should_receive(:srand).ordered.with(123)
+          list.should_receive(:shuffle).ordered.and_return([2, 4, 1, 3])
+          Kernel.should_receive(:srand).ordered.with(no_args)
+          expect(list.ordered).to eq([2, 4, 1, 3])
+        end
+      end
+
       context 'given "random:123"' do
         before { config.order = 'random:123' }
 
@@ -1391,7 +1410,9 @@ def metadata_hash(*args)
         it 'sets up random ordering' do
           RSpec.stub(:configuration => config)
           list = [1, 2, 3, 4].extend(Extensions::Ordered::Examples)
-          Kernel.should_receive(:rand).and_return(3, 1, 4, 2)
+          Kernel.should_receive(:srand).ordered.with(123)
+          list.should_receive(:shuffle).ordered.and_return([2, 4, 1, 3])
+          Kernel.should_receive(:srand).ordered.with(no_args)
           expect(list.ordered).to eq([2, 4, 1, 3])
         end
       end