[rubygems/rubygems] Use globals variables for standard input/output

Replace use of `STDIN`, `STDOUT` and `STDERR` constants by their
`$stdin`, `$stdout` and `$stderr` global variable equivalents.

This enables easier testing via standard means, such as `assert_output`
for minitest or `expect { print 'foo' }.to output.to_stdout` for RSpec
test suites.

https://github.com/rubygems/rubygems/commit/a0a6fc1b76

1 files changed, 19 insertions, 0 deletions

diff --git a/test/rubygems/test_gem_console_ui.rb b/test/rubygems/test_gem_console_ui.rb
new file mode 100644
index 0000000000..b8a619625f
--- /dev/null
+++ b/test/rubygems/test_gem_console_ui.rb
@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+require_relative "helper"
+require "rubygems/user_interaction"
+
+class TestGemConsoleUI < Gem::TestCase
+  def test_output_can_be_captured_by_test_unit
+    output = capture_output do
+      ui = Gem::ConsoleUI.new
+
+      ui.alert_error "test error"
+      ui.alert_warning "test warning"
+      ui.alert "test alert"
+    end
+
+    assert_equal "INFO:  test alert\n", output.first
+    assert_equal "ERROR:  test error\n" + "WARNING:  test warning\n", output.last
+  end
+end