1 files changed, 84 insertions, 0 deletions
diff --git a/spec/ruby/core/array/repeated_combination_spec.rb b/spec/ruby/core/array/repeated_combination_spec.rb
new file mode 100644
index 0000000000..b62382024a
--- /dev/null
+++ b/spec/ruby/core/array/repeated_combination_spec.rb
@@ -0,0 +1,84 @@
+require_relative '../../spec_helper'
+
+describe "Array#repeated_combination" do
+  before :each do
+    @array = [10, 11, 12]
+  end
+
+  it "returns an enumerator when no block is provided" do
+    @array.repeated_combination(2).should be_an_instance_of(Enumerator)
+  end
+
+  it "returns self when a block is given" do
+    @array.repeated_combination(2){}.should equal(@array)
+  end
+
+  it "yields nothing for negative length and return self" do
+    @array.repeated_combination(-1){ fail }.should equal(@array)
+    @array.repeated_combination(-10){ fail }.should equal(@array)
+  end
+
+  it "yields the expected repeated_combinations" do
+    @array.repeated_combination(2).to_a.sort.should == [[10, 10], [10, 11], [10, 12], [11, 11], [11, 12], [12, 12]]
+    @array.repeated_combination(3).to_a.sort.should == [[10, 10, 10], [10, 10, 11], [10, 10, 12], [10, 11, 11], [10, 11, 12],
+                                                        [10, 12, 12], [11, 11, 11], [11, 11, 12], [11, 12, 12], [12, 12, 12]]
+  end
+
+  it "yields [] when length is 0" do
+    @array.repeated_combination(0).to_a.should == [[]] # one repeated_combination of length 0
+    [].repeated_combination(0).to_a.should == [[]] # one repeated_combination of length 0
+  end
+
+  it "yields nothing when the array is empty and num is non zero" do
+    [].repeated_combination(5).to_a.should == [] # one repeated_combination of length 0
+  end
+
+  it "yields a partition consisting of only singletons" do
+    @array.repeated_combination(1).sort.to_a.should == [[10],[11],[12]]
+  end
+
+  it "accepts sizes larger than the original array" do
+    @array.repeated_combination(4).to_a.sort.should ==
+      [[10, 10, 10, 10], [10, 10, 10, 11], [10, 10, 10, 12],
+       [10, 10, 11, 11], [10, 10, 11, 12], [10, 10, 12, 12],
+       [10, 11, 11, 11], [10, 11, 11, 12], [10, 11, 12, 12],
+       [10, 12, 12, 12], [11, 11, 11, 11], [11, 11, 11, 12],
+       [11, 11, 12, 12], [11, 12, 12, 12], [12, 12, 12, 12]]
+  end
+
+  it "generates from a defensive copy, ignoring mutations" do
+    accum = []
+    @array.repeated_combination(2) do |x|
+      accum << x
+      @array[0] = 1
+    end
+    accum.sort.should == [[10, 10], [10, 11], [10, 12], [11, 11], [11, 12], [12, 12]]
+  end
+
+  describe "when no block is given" do
+    describe "returned Enumerator" do
+      describe "size" do
+        it "returns 0 when the combination_size is < 0" do
+          @array.repeated_combination(-1).size.should == 0
+          [].repeated_combination(-2).size.should == 0
+        end
+
+        it "returns 1 when the combination_size is 0" do
+          @array.repeated_combination(0).size.should == 1
+          [].repeated_combination(0).size.should == 1
+        end
+
+        it "returns the binomial coefficient between combination_size and array size + combination_size -1" do
+          @array.repeated_combination(5).size.should == 21
+          @array.repeated_combination(4).size.should == 15
+          @array.repeated_combination(3).size.should == 10
+          @array.repeated_combination(2).size.should == 6
+          @array.repeated_combination(1).size.should == 3
+          @array.repeated_combination(0).size.should == 1
+          [].repeated_combination(0).size.should == 1
+          [].repeated_combination(1).size.should == 0
+        end
+      end
+    end
+  end
+end