Merge pull request #1751 from cubicdaiya/issues/test_for_instance_variable_defined_question

Add test for Kernel#instance_variable_defined?

test/t/kernel.rb

@@ -264,6 +264,16 @@ assert('Kernel#inspect', '15.3.1.3.17') do
   assert_equal "main", s
 end
 
+assert('Kernel#instance_variable_defined?', '15.3.1.3.20') do
+  o = Object.new
+  o.instance_variable_set(:@a, 1)
+
+  assert_equal o.instance_variable_defined?("@a"), true
+  assert_equal o.instance_variable_defined?("@b"), false
+  assert_equal o.instance_variable_defined?("@a"[0,2]), true
+  assert_equal o.instance_variable_defined?("@abc"[0,2]), true
+end
+
 assert('Kernel#instance_variables', '15.3.1.3.23') do
   o = Object.new
   o.instance_eval do