How to use custom flag in tests (with `testify/suite`)

I want to add custom flags for my Go tests that use testify/suite. It looks like from this thread that it can only be in TestMain() (init() if it is before Go 1.13). However, with the testify/suite pacakge, TestMain() is not quite an option. I have tried declaring the flags in SeupSuite() and TestMyTestSuite() which seems to be a corresponding TestMain() but both returned the error flag provided but not defined: -mycustomflag. Below is the sample code. Any suggestion will be appreciated!

my_test.go:

package main

import (
	"flag"
	"fmt"
	"github.com/stretchr/testify/suite"
	"testing"
)

type MyTestSuite struct {
	suite.Suite
}

func (suite *MyTestSuite) SetupSuite() {
	flagBoolPtr := flag.Bool("mycustomflag", false, "this is a bool flag")
	flag.Parse()
	fmt.Printf("my flag is set to: %t", *flagBoolPtr)
}

func TestMyTestSuite(t *testing.T) {
	// flagBoolPtr := flag.Bool("mycustomflag", false, "this is a bool flag")
	// flag.Parse()
	// fmt.Printf("my flag is set to: %t", *flagBoolPtr)
	suite.Run(t, new(MyTestSuite))
}

func (suite *MyTestSuite) TestBuildClosure() {
	fmt.Println("my test")
}

This is the command I used:

go test my_test.go -mycustomflag

The test binary generated by go test is already using the flag package internally and calls flag.Parse() during normal operation.
Define the flag variable as global (✳️) so they are known before running flag.Parse().

type MyTestSuite struct {
	suite.Suite
}

// ✳️
var flagBoolPtr = flag.Bool("mycustomflag", false, "this is a bool flag")

func (suite *MyTestSuite) SetupSuite() {
	fmt.Printf("my flag in SetupSuite: %t\n", *flagBoolPtr)
}

func TestMyTestSuite(t *testing.T) {
	fmt.Printf("my flag in test: %t\n", *flagBoolPtr)
	suite.Run(t, new(MyTestSuite))
}

func (suite *MyTestSuite) TestBuildClosure() {
	fmt.Println("my test")
}

go test -v my_test.go -mycustomflag

=== RUN   TestMyTestSuite
my flag in test: true
my flag in SetupSuite: true
=== RUN   TestMyTestSuite/TestBuildClosure
my test
--- PASS: TestMyTestSuite (0.00s)
    --- PASS: TestMyTestSuite/TestBuildClosure (0.00s)
PASS

> Although what if I have multiple testsuites aka multiple files in the same package? And I want to use this flag for all testsuites? Since we can define the variable and the flag only once, how can I make sure this declaration in this specific testsuite gets executed first?

To run test separately in the package, create a file for the package contains only with required flag (✳️) and compile single test with file, which contains flags

.
├── my_test.go
├── other_my_test.go
└── flag_test.go // ✳️

👇🏻 flag_test.go

package any

import "flag"

var flagBoolPtr = flag.Bool("mycustomflag", false, "this is a bool flag")

go test -v flag_test.go my_test.go -mycustomflag

also you can run all tests with required flag

 go test -v ./... -mycustomflag