Find second last Wednesday of the Month

wednesday.go

package utils

import "time"

func SecondLastWednesday(year int, month time.Month) int {
	t := time.Date(year, month, 1, 0, 0, 0, 0, time.Local)
	lastOfMonth := t.AddDate(0, 1, -1)
	if lastOfMonth.Weekday() == 3 {
		// Last day is a Wednesday
		return (lastOfMonth.Day() - 7)
	} else if lastOfMonth.Weekday() > 3 {
		// Later than a Wednesday
		return lastOfMonth.Day() - (int(lastOfMonth.Weekday()) - 3) - 7
	} else {
		// Earlier than a Wednesday. Find what would've been the next 
		return (lastOfMonth.Day() + (3 - int(lastOfMonth.Weekday()))) - 14
	}
}

// test

package utils

import (
	"testing"
	"time"
)

type wednesdayTest struct {
	year     int
	month    time.Month
	expected int
}

var addTests = []wednesdayTest{
	{2021, time.September, 22}, // Last day a Thursday
	{2020, time.October, 21},   // Last day a Saturday
	{2020, time.March, 18},     // Last day is a Tueday
	{2023, time.May, 24},       // Last day a Wednesday
}

func TestSecondLastWednesday(t *testing.T) {
	for _, test := range addTests {
		if output := SecondLastWednesday(test.year, test.month); output != test.expected {
			t.Errorf("Output %d not equal to expected %d", output, test.expected)
		}
	}
}