[ruby/reline] Add a test for suppressing crash when dynamic prompt returns empty

ref. https://github.com/ruby/reline/pull/262

b98bc3c329

test/reline/yamatanooroti/multiline_repl

@@ -24,6 +24,9 @@ opt.on('--broken-dynamic-prompt') {
     }
   }
 }
+opt.on('--dynamic-prompt-returns-empty') {
+  Reline.prompt_proc = proc { |l| [] }
+}
 opt.on('--auto-indent') {
   AutoIndent.new
 }

test/reline/yamatanooroti/test_rendering.rb

@@ -706,6 +706,19 @@ begin
       EOC
     end
 
+    def test_dynamic_prompt_returns_empty
+      start_terminal(5, 20, %W{ruby -I#{@pwd}/lib #{@pwd}/test/reline/yamatanooroti/multiline_repl --dynamic-prompt-returns-empty}, startup_message: 'Multiline REPL.')
+      write("def hoge\nend\n")
+      close
+      assert_screen(<<~EOC)
+        Multiline REPL.
+        prompt> def hoge
+        prompt> end
+        => :hoge
+        prompt>
+      EOC
+    end
+
     private def write_inputrc(content)
       File.open(@inputrc_file, 'w') do |f|
         f.write content