QuickData is a (very hacky) plumbing class that loads realistic test data from any SObject. Mockaroo provides a very pleasant and powerful toolkit for creating test data. QuickData generates data from a saved Mockaroo schema and inserts it as is into Salesforce.
You'll require a free account with Mockaroo to be able to save schemas and use the API. Once you set up a free account, start building fields for your SObject. You can see my sample schema for Lead at https://www.mockaroo.com/20689c00. The output format must be configured as a JSON Array, as in my example. Your Mockaroo field names must exactly match your Salesforce field names. If you'd like to hide a field in the schema from your output to salesforce, put two __s in front of it's name, and it will not be mapped.
QuickData.createRecords('MOCKAROOAPIKEY','20689c00',20,List<Lead>.class);
The fourth parameter of the call is the Type
object for a list of your SObject (e.g. List<Opportunity>.class
or List<Shark__c>.class
)