Added a test to make sure ECDSA.sign returns nil if r is 0.

Author: DavidEGrayson

spec/sign_spec.rb

@@ -1,6 +1,10 @@
 require 'spec_helper'
 
 describe 'ECDSA.sign' do
+  it 'returns nil if r is zero' do
+    expect(ECDSA.sign(Davidp16d1, 333, 222, 1)).to eq nil
+  end
+
   it 'returns nil if s is zero' do
     group = ECDSA::Group::Secp112r2
     private_key = 1

spec/spec_helper.rb

@@ -5,3 +5,13 @@
 
 $LOAD_PATH << 'lib'
 require 'ecdsa'
+
+Davidp16d1 = ECDSA::Group.new(
+  name: 'davidp16d1',
+  p: 0xff8f,
+  a: -3,
+  b: 0x2ccd,
+  g: [0, 0x5455],
+  n: 0x7efb,
+  h: 2,
+)