Add spec for Binding#irb.

Author: nirvdrum

spec/ruby/core/binding/fixtures/irb.rb

@@ -0,0 +1,3 @@
+a = 10
+
+binding.irb

spec/ruby/core/binding/irb_spec.rb

@@ -0,0 +1,17 @@
+require_relative '../../spec_helper'
+
+ruby_version_is "2.5" do
+  describe "Binding#irb" do
+    it "creates an IRB session with the binding in scope" do
+      irb_fixture = fixture __FILE__, "irb.rb"
+
+      out = IO.popen([*ruby_exe, irb_fixture], "r+") do |pipe|
+        pipe.puts "a ** 2"
+        pipe.puts "exit"
+        pipe.readlines.map(&:chomp)
+      end
+
+      out[-3..-1].should == ["a ** 2", "100", "exit"]
+    end
+  end
+end