Month: handle edge case

lib/calrom/date_range.rb

@@ -14,7 +14,13 @@ def to_s
 
   class Month < DateRange
     def initialize(year, month)
-      super Date.new(year, month, 1), Date.new(year, month + 1, 1) - 1
+      next_month_beginning =
+        if month == 12
+          Date.new(year + 1, 1, 1)
+        else
+          Date.new(year, month + 1, 1)
+        end
+      super Date.new(year, month, 1), next_month_beginning - 1
     end
 
     def to_s

spec/calrom_spec.rb

@@ -4,8 +4,4 @@
   it "has a version number" do
     expect(Calrom::VERSION).not_to be nil
   end
-
-  it "does something useful" do
-    expect(false).to eq(true)
-  end
 end

spec/date_range_spec.rb

@@ -0,0 +1,18 @@
+require 'spec_helper'
+
+describe 'date ranges' do
+  describe Calrom::Month do
+    1.upto(12) do |i|
+      it "supports month #{i}" do
+        described_class.new(2000, i)
+      end
+
+      it "yields Dates of the given year and month #{i}" do
+        described_class.new(2000, i).each do |date|
+          expect(date.year).to be 2000
+          expect(date.month).to be i
+        end
+      end
+    end
+  end
+end