If you want to know how to set text in CKEDITOR using selenium than here is the way please go through this.

WebDriver driver = new FireFoxDriver()
JavascriptExecutor js;
    if ((driver) instanceof JavascriptExecutor) {
        js = (JavascriptExecutor)(driver);
    js.executeScript("CKEDITOR.instances['ckEditorId'].insertHtml('Hi How are you.');");

First-of-all create an instance of WebDriver and provide a name or id to CKEDITOR. Here “ckEditorId” is an id of CKEDITOR. To executeScript create an instance of javaScriptExecutor and we can pass our text by using insertHtml.
This approach could be used in Geb or Cucumber automated functional testing if selenium is used in that.