in src/main/java/org/apache/sling/testing/clients/util/HttpUtils.java [111:126]
public static String buildDefaultErrorMessage(SlingHttpResponse resp) {
String content = resp.getContent();
// if no response content is available
if (content == null) return "";
String errorMsg = resp.getSlingMessage();
errorMsg = (errorMsg == null || errorMsg.length() == 0)
// any other returned content
? " Response Content:\n" + content
// response message from sling response
: "Error Message: \n" + errorMsg;
return errorMsg;
}