Increment batch numbers if not set manually (fixes #42)

lib/ach/ach_file.rb

@@ -25,7 +25,11 @@ def initialize data=nil
     def to_s
       records = []
       records << @header
-      @batches.each { |b| records += b.to_ach }
+
+      @batches.each_with_index do |batch, index|
+        batch.header.batch_number ||= index + 1
+        records += batch.to_ach
+      end
       records << @control
 
       nines_needed = 10 - (records.length % 10)

lib/ach/records/batch_header.rb

@@ -33,6 +33,6 @@ class BatchHeader < Record
     field :originating_dfi_identification, String,
         nil, nil, /\A\d{8}\z/
 
-    field :batch_number, Integer, lambda { |f| sprintf('%07d', f)}, 1
+    field :batch_number, Integer, lambda { |f| sprintf('%07d', f)}, nil
   end
 end

spec/ach/ach_file_spec.rb

@@ -47,6 +47,26 @@ def add_detail batch
   end
 
   describe '#to_s' do
+    describe 'incrementing batch numbers' do
+      before(:each) do
+        add_batch ach_file, 1
+        add_batch ach_file, 1
+        add_batch ach_file, 1
+      end
+
+      context 'batch numbers not set' do
+        it 'increments batch numbers' do
+          lines = ach_file.to_s.split("\r\n")
+          expect(lines[1][-1]).to eq('1')
+          expect(lines[3][-1]).to eq('1')
+          expect(lines[4][-1]).to eq('2')
+          expect(lines[6][-1]).to eq('2')
+          expect(lines[7][-1]).to eq('3')
+          expect(lines[9][-1]).to eq('3')
+        end
+      end
+    end
+
     describe 'padding with 9s' do
       let(:nines) { '9' * 94 }