diff --git a/test/irb/test_ruby-lex.rb b/test/irb/test_ruby-lex.rb
new file mode 100644
index 0000000000..f7d331bc24
--- /dev/null
+++ b/test/irb/test_ruby-lex.rb
@@ -0,0 +1,18 @@
+# frozen_string_literal: false
+require 'test/unit'
+require 'irb/ruby-lex'
+
+module TestIRB
+  class TestRubyLex < Test::Unit::TestCase
+    def setup
+      @scanner = RubyLex.new
+    end
+
+    def test_set_input_proc
+      called = false
+      @scanner.set_input(self) {|x| called = true; nil}
+      assert_nil(@scanner.lex)
+      assert(called)
+    end
+  end
+end