Resurrect tests for StringScanner#rest?

that has not been obsolete.

Partially reverting ruby/ruby#15049.

Author: k0kubun

library/stringscanner/rest_spec.rb

@@ -25,3 +25,24 @@
   it_behaves_like :extract_range_matched, :rest
 
 end
+
+describe "StringScanner#rest?" do
+  before :each do
+    @s = StringScanner.new("This is a test")
+  end
+
+  it "returns true if there is more data in the string" do
+    @s.rest?.should be_true
+    @s.scan(/This/)
+    @s.rest?.should be_true
+  end
+
+  it "returns false if there is no more data in the string" do
+    @s.terminate
+    @s.rest?.should be_false
+  end
+
+  it "is the opposite of eos?" do
+    @s.rest?.should_not == @s.eos?
+  end
+end