Add tests and documentation for capital_letter

We didn't have time for this during the The Biggest Mobprogramming
session ever at RubyConfBY 2019: https://rubyconference.by

@dmitriy-kiriyenko implemented it in
https://github.com/JEG2/highline/pull/242, so I cherry-picked it from
there.

Co-authored-by: Dmitriy Kiriyenko <dmitriy.kiriyenko@gmail.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/test/test_menu.rb b/test/test_menu.rb
index 6278c7c..2a8cbaf 100755
--- a/test/test_menu.rb
+++ b/test/test_menu.rb
@@ -539,6 +539,19 @@ class TestMenu < Minitest::Test
     assert_equal(:load, selected)
   end
 
+  def test_select_by_capital_letter
+    @input << "B\n"
+    @input.rewind
+
+    selected = @terminal.choose do |menu|
+      menu.index = :capital_letter
+      menu.choice   :save
+      menu.choice   :load
+      menu.choice   :quit
+    end
+    assert_equal(:load, selected)
+  end
+
   def test_shell
     @input << "save --some-option my_file.txt\n"
     @input.rewind