bbasata · November 5, 2011 02:04 · Nov 5, 2011
diff --git a/factorial_spec.rb b/factorial_spec.rb
@@ -0,0 +1,27 @@
+class Integer
+  def factorial
+    raise if self < 0
+    self > 0 ? (1..self).reduce(&:*) : 1
+  end
+end
+
+describe Integer, '#factorial' do
+  context "for values larger than 1" do
+    example { 2.factorial.should == 2*1 }
+    example { 3.factorial.should == 3*2*1 }
+    example { 4.factorial.should == 4*3*2*1 }
+    example { 8.factorial.should == 8*7*6*5*4*3*2*1 }
+  end
+
+  context "for 1" do
+    example { 1.factorial.should == 1 }
+  end
+
+  context "for 0" do
+    example { 0.factorial.should == 1 }
+  end
+
+  context "for negative numbers" do
+    example { expect { -1.factorial }.to raise_error }
+  end
+end