Tests stemming for hook_search_preprocess().
function testPreprocessStemming() {
  // Create a node.
  $node = $this
    ->drupalCreateNode(array(
    'title' => 'we are testing',
    'body' => array(
      'en' => array(
        array(),
      ),
    ),
    'langcode' => 'en',
  ));
  // First update the index. This does the initial processing.
  node_update_index();
  // Then, run the shutdown function. Testing is a unique case where indexing
  // and searching has to happen in the same request, so running the shutdown
  // function manually is needed to finish the indexing process.
  search_update_totals();
  // Search for the title of the node with a POST query.
  $edit = array(
    'or' => 'testing',
  );
  $this
    ->drupalPost('search/node', $edit, t('Advanced search'));
  // Check if the node has been found.
  $this
    ->assertText('Search results');
  $this
    ->assertText('we are testing');
  // Search for the same node using a different query.
  $edit = array(
    'or' => 'test',
  );
  $this
    ->drupalPost('search/node', $edit, t('Advanced search'));
  // Check if the node has been found.
  $this
    ->assertText('Search results');
  $this
    ->assertText('we are testing');
}