Add test cases

test/test_all.rb

@@ -5,3 +5,4 @@ $LOAD_PATH.unshift(File.expand_path("ext"))
 require 'digest/keccak'
 require File.expand_path('test/test_usage')
 require File.expand_path('test/test_vectors')
+require File.expand_path('test/test_new')

test/test_new.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+require 'test/unit'
+
+class KeccakNewTests < Test::Unit::TestCase
+  def test_singleton_method_hexdigest_256_empty
+    result = Digest::Keccak.hexdigest '', 256
+    assert_instance_of String, result
+    assert_equal 'c5d2460186f7233c927e7db2dcc703c0' \
+                 'e500b653ca82273b7bfad8045d85a470',
+                 result
+  end
+
+  def test_singleton_method_hexdigest_256_sample
+    result = Digest::Keccak.hexdigest 'sample', 256
+    assert_instance_of String, result
+    assert_equal 'b80204f7e9243e4fca5489740ccd31dc' \
+                 'd0a54619a7f4165cee73c191ef7271a1',
+                 result
+  end
+end