Golang fuzz testing and also property-based testing.

fuzz_property_test.go

package main

import (
	"testing"

	"pgregory.net/rapid"
)

// Sum adds two numbers.
func Sum(a, b int64) (total int64) {
	return a + b
}

func TestSum(t *testing.T) {
	// go test -race -count=1 ./...

	rapid.Check(t, func(t *rapid.T) {
		a := rapid.Int64().Draw(t, "a")
		b := rapid.Int64().Draw(t, "b")

		tt := Sum(a, b)
		if tt < a { // todo: There's bug here since total of negative number and postivive might be less than one of the numbers.
			t.Fatalf("got: %d. expected total to be greater than a", tt)
		}
	})
}

func FuzzSum(f *testing.F) {
	// go test -count=1 -fuzz ./...

	// f.Add(...)  // Use f.Add to provide a seed corpus

	f.Fuzz(func(t *testing.T, a, b int64) {
		tt := Sum(a, b)
		if tt < a { // todo: There's bug here since total of negative number and postivive might be less than one of the numbers.
			t.Fatalf("got: %d. expected total to be greater than a", tt)
		}

		if Sum(a, b) != Sum(b, a) {
			t.Fatal("addition should be commutative")
		}
	})
}