CF Stress is a community driven, highly customizable, no-code tool to stress test
You can get the smallest possible counter-example for your failing submissions, with > 95% accuracy.
You control all the parameters of the generator without writing a single line of code.
Just plug in your submission ID, tune the parameters and wait for the ticket to be processed.
It also has support for non-unique answers and interactive problems.
You can also get as many sample test cases as you want. You can also customize these samples by restricting the array length, range of array values, etc.