Tests t() functionality.
function testT() {
  $text = t('Simple text');
  $this
    ->assertEqual($text, 'Simple text', 't leaves simple text alone.');
  $text = t('Escaped text: @value', array(
    '@value' => '<script>',
  ));
  $this
    ->assertEqual($text, 'Escaped text: <script>', 't replaces and escapes string.');
  $text = t('Placeholder text: %value', array(
    '%value' => '<script>',
  ));
  $this
    ->assertEqual($text, 'Placeholder text: <em class="placeholder"><script></em>', 't replaces, escapes and themes string.');
  $text = t('Verbatim text: !value', array(
    '!value' => '<script>',
  ));
  $this
    ->assertEqual($text, 'Verbatim text: <script>', 't replaces verbatim string as-is.');
}