The Drupal 8 version of devel/devel_generate module has a good example of this.
  $edit_node = array(
    'nid' => NULL, 
    'type' => $node_type, 
    'uid' => $users[array_rand($users)], 
    'revision' => mt_rand(0, 1), 
    'status' => TRUE, 
    'promote' => mt_rand(0, 1), 
    'created' => REQUEST_TIME - mt_rand(0, $results['time_range']), 
    'langcode' => devel_generate_get_langcode($results),
  );
  if ($type->has_title) {
    // We should not use the random function if the value is not random
    if ($results['title_length'] < 2) {
      $edit_node['title'] = devel_create_greeking(1, TRUE);
    }
    else {
      $edit_node['title'] = devel_create_greeking(mt_rand(1, $results['title_length']), TRUE);
    }
  }
  else {
    $edit_node['title'] = '';
  }
  // @todo Remove once comment become field. http://drupal.org/node/731724
  if (Drupal::moduleHandler()->moduleExists('comment')) {
    $edit_node['comment'] = variable_get('comment_' . $node_type, COMMENT_NODE_OPEN);
  }
  $node = entity_create('node', $edit_node);
Using formatted text
Using grep with before/after code lines helped me figure out how to add a node with 'full_html'.
Search the Drupal core code with this :
$ cd drupal/core
$ grep -B 5 -A 5 -r entity_create.*node * > /tmp/temp-grep.txt
Then, open up /tmp/temp-grep.txt in a text editor.  Poke around there a bit and you'll see this :
--
modules/editor/src/Tests/EditorFileUsageTest.php-    $body_value .= '<img src="awesome-llama.jpg" data-editor-file-uuid="invalid-editor-file-uuid-value" />';
modules/editor/src/Tests/EditorFileUsageTest.php-    // Test handling of a non-existing UUID.
modules/editor/src/Tests/EditorFileUsageTest.php-    $body_value .= '<img src="awesome-llama.jpg" data-editor-file-uuid="30aac704-ba2c-40fc-b609-9ed121aa90f4" />';
modules/editor/src/Tests/EditorFileUsageTest.php-    // Test editor_entity_insert(): increment.
modules/editor/src/Tests/EditorFileUsageTest.php-    $this->createUser();
modules/editor/src/Tests/EditorFileUsageTest.php:    $node = entity_create('node', array(
modules/editor/src/Tests/EditorFileUsageTest.php-      'type' => 'page',
modules/editor/src/Tests/EditorFileUsageTest.php-      'title' => 'test',
modules/editor/src/Tests/EditorFileUsageTest.php-      'body' => array(
modules/editor/src/Tests/EditorFileUsageTest.php-        'value' => $body_value,
modules/editor/src/Tests/EditorFileUsageTest.php-        'format' => 'filtered_html',
--
Note how 'body' now becomes an array with a 'value' and a 'format'.