YWC question

card_at.go

package cardat

import (
	"fmt"
)

func cardAt(n int) string {
	if n < 0 || n > 51 {
		return "Out of range"
	}
	suits := []byte{'C', 'D', 'H', 'S'}
	ranks := []byte{'2', '3', '4', '5', '6', '7', '8', '9', 'O', 'J', 'Q', 'K', 'A'}
	return fmt.Sprintf("%c%c", ranks[n%13], suits[n/13])
}

card_at_test.go

package cardat

import (
	"fmt"
	"testing"
)

func TestCardAt(t *testing.T) {
	testCases := []struct {
		n        int
		expected string
	}{
		{
			n:        -1,
			expected: "Out of range",
		},
		{
			n:        0,
			expected: "2C",
		},
		{
			n:        1,
			expected: "3C",
		},
		{
			n:        34,
			expected: "OH",
		},
		{
			n:        35,
			expected: "JH",
		},
		{
			n:        52,
			expected: "Out of range",
		},
	}
	for _, tC := range testCases {
		desc := fmt.Sprintf("cardAt should return %s when n = %d", tC.expected, tC.n)
		t.Run(desc, func(t *testing.T) {
			actual := cardAt(tC.n)
			if actual != tC.expected {
				t.Errorf("expected %s but got %s", tC.expected, actual)
			}
		})
	}
}