add tests for method cache.

test/ruby/test_method_cache.rb

@@ -0,0 +1,65 @@
+# frozen_string_literal: true
+require 'test/unit'
+
+class TestMethodCache < Test::Unit::TestCase
+  def test_undef
+    # clear same
+    c0 = Class.new do
+      def foo; end
+      undef foo
+    end
+
+    assert_raise(NoMethodError) do
+      c0.new.foo
+    end
+
+    c0.class_eval do
+      def foo; :ok; end
+    end
+
+    assert_equal :ok, c0.new.foo
+  end
+
+  def test_undef_with_subclasses
+    # with subclasses
+    c0 = Class.new do
+      def foo; end
+      undef foo
+    end
+
+    c1 = Class.new(c0)
+
+    assert_raise(NoMethodError) do
+      c0.new.foo
+    end
+
+    c0.class_eval do
+      def foo; :ok; end
+    end
+
+    assert_equal :ok, c0.new.foo
+  end
+
+  def test_undef_with_subclasses_complicated
+    c0 = Class.new{ def foo; end }
+    c1 = Class.new(c0){ undef foo }
+    c2 = Class.new(c1)
+    c3 = Class.new(c2)
+    c4 = Class.new(c3)
+
+    assert_raise(NoMethodError) do
+      c3.new.foo
+    end
+
+    c2.class_eval do
+      def foo; :c2; end
+    end
+
+    assert_raise(NoMethodError) do
+      c1.new.foo
+    end
+
+    assert_equal :c2, c3.new.foo
+  end
+end
+