Added tests for setting ivars on frozen objs

test/ruby/test_frozen.rb

@@ -0,0 +1,30 @@
+# frozen_string_literal: false
+require 'test/unit'
+
+class TestFrozen < Test::Unit::TestCase
+  def test_setting_ivar_on_frozen_obj
+    obj = Object.new
+    obj.freeze
+    assert_raise(FrozenError) { obj.instance_variable_set(:@a, 1) }
+  end
+
+  def test_setting_ivar_on_frozen_obj_with_ivars
+    obj = Object.new
+    obj.instance_variable_set(:@a, 1)
+    obj.freeze
+    assert_raise(FrozenError) { obj.instance_variable_set(:@b, 1) }
+  end
+
+  def test_setting_ivar_on_frozen_string
+    str = "str"
+    str.freeze
+    assert_raise(FrozenError) { str.instance_variable_set(:@a, 1) }
+  end
+
+  def test_setting_ivar_on_frozen_string_with_ivars
+    str = "str"
+    str.instance_variable_set(:@a, 1)
+    str.freeze
+    assert_raise(FrozenError) { str.instance_variable_set(:@b, 1) }
+  end
+end