1 files changed, 30 insertions, 0 deletions
diff --git a/spec/lib/confidence_intervals.rb b/spec/lib/confidence_intervals.rb
new file mode 100644
index 000000000..cb8717f3d
--- /dev/null
+++ b/spec/lib/confidence_intervals.rb
@@ -0,0 +1,30 @@
+require 'confidence_intervals'
+
+describe "ci_bounds" do
+
+  describe "when passed all successes" do
+    it "should never return a high CI above 1" do
+      ci = ci_bounds 16, 16, 0.01
+      ci[1].should be <= 1
+    end
+  end
+
+  describe "when passed all failures" do
+    it "should never return a low CI below 0" do
+      ci = ci_bounds 0, 10, 0.05
+      ci[0].should be >= 0
+    end
+  end
+
+  describe "when passed 4 out of 10 successes (with 0.05 power)" do
+    it "should return the correct Wilson's interval" do
+      # The expected results here were taken from an online
+      # calculator:
+      #   http://www.vassarstats.net/prop1.html
+      ci = ci_bounds 7, 10, 0.05
+      ci[0].should be_within(0.001).of(0.3968)
+      ci[1].should be_within(0.001).of(0.8922)
+    end
+  end
+
+end