add test for String#sum.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@6985 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_string.rb

@@ -0,0 +1,19 @@
+require 'test/unit'
+
+class TestString < Test::Unit::TestCase
+  def check_sum(str, bits=16)
+    sum = 0
+    str.each_byte {|c| sum += c}
+    sum = sum & ((1 << bits) - 1) if bits != 0
+    assert_equal(sum, str.sum(bits))
+  end
+  def test_sum
+    assert_equal(0, "".sum)
+    assert_equal(294, "abc".sum)
+    check_sum("abc")
+    check_sum("\x80")
+    8.upto(70) {|bits|
+      check_sum("xyz", bits)
+    }
+  end
+end