testing sort.Slice() https://stackoverflow.com/questions/73056418/how-do-you-write-a-test-for-sort-slice

go.mod

module gist.github.com/e3b13265d24471651e02f7d7a42e7d2c

go 1.18

main.go

// main.go
package main

import (
	"fmt"
	"sort"
)

type Person struct {
	Name string
	Age  int
}

func comparePeopleByName(people []Person) func(int, int) bool {
	return func(i, j int) bool {
		return people[i].Name < people[j].Name
	}
}

func comparePeopleByAge(people []Person) func(int, int) bool {
	return func(i, j int) bool {
		return people[i].Age < people[j].Age
	}
}

func main() {
	people := []Person{
		{"Gopher", 7},
		{"Alice", 55},
		{"Vera", 24},
		{"Bob", 75},
	}
	sort.Slice(people, comparePeopleByName(people))
	fmt.Println("By name:", people)

	sort.Slice(people, comparePeopleByAge(people))
	fmt.Println("By age:", people)
}

main_test.go

// main_test.go
package main

import "testing"

func TestComparePeopleByName(t *testing.T) {
	testCases := []struct {
		desc     string
		a, b     Person
		expected bool
	}{
		{"a < b", Person{"bob", 1}, Person{"krabs", 2}, true},
		{"a > b", Person{"krabs", 1}, Person{"bob", 2}, false},
		{"a = a", Person{"plankton", 1}, Person{"plankton", 2}, false},
	}

	for _, testCase := range testCases {
		t.Run(testCase.desc, func(t *testing.T) {
			people := []Person{testCase.a, testCase.b}
			got := comparePeopleByName(people)(0, 1)
			if testCase.expected != got {
				t.Errorf("expected %v, got %v", testCase.expected, got)
			}
		})
	}
}

func TestComparePeopleByAge(t *testing.T) {
	testCases := []struct {
		desc     string
		a, b     Person
		expected bool
	}{
		{"a < b", Person{"sandy", 10}, Person{"patrick", 20}, true},
		{"a > b", Person{"sandy", 30}, Person{"patrick", 20}, false},
		{"a = b", Person{"sandy", 90}, Person{"patrick", 90}, false},
	}

	for _, testCase := range testCases {
		t.Run(testCase.desc, func(t *testing.T) {
			people := []Person{testCase.a, testCase.b}
			got := comparePeopleByAge(people)(0, 1)
			if testCase.expected != got {
				t.Errorf("expected %v, got %v", testCase.expected, got)
			}
		})
	}
}