Make Kernel.print spec compliant

spec/core/kernel/print_spec.rb

@@ -0,0 +1,24 @@
+require_relative '../../spec_helper'
+require_relative 'fixtures/classes'
+
+describe "Kernel#print" do
+  it "is a private method" do
+    Kernel.should have_private_instance_method(:print)
+  end
+
+  it "delegates to $stdout" do
+    -> { print :arg }.should output("arg")
+  end
+
+  it "prints $_ when no arguments are given" do
+    orig_value = $_
+    $_ = 'foo'
+    -> { print }.should output("foo")
+  ensure
+    $_ = orig_value
+  end
+end
+
+describe "Kernel.print" do
+  it "needs to be reviewed for spec completeness"
+end

src/kernel_module.cpp

@@ -510,16 +510,8 @@ Value KernelModule::p(Env *env, Args args) {
 Value KernelModule::print(Env *env, Args args) {
     auto _stdout = env->global_get("$stdout"_s);
     assert(_stdout);
-    // NATFIXME: This prevents crashes when $stdout is set to an object that
-    // doesn't have a write method.  Technically this should be done when
-    // setting the global, but we dont have a hook for that yet, so this will
-    // do for now.
-    if (!_stdout->respond_to(env, "write"_s)) {
-        env->raise("TypeError", "$stdout must have write method, {} given", _stdout->klass()->inspect_str());
-    }
-    if (!_stdout->respond_to(env, "print"_s)) {
-        env->raise("TypeError", "$stdout must have print method, {} given", _stdout->klass()->inspect_str());
-    }
+    if (args.size() == 0)
+        args = Args { env->global_get("$_"_s) };
     // NATFIXME: Kernel.print should actually call IO.print and not
     // IO.write, but for now using IO.print causes crashes.
     // return _stdout->send(env, "print"_s, args);