[bug report] flag provided but not defined: -test.v

[fwhezfwhez]

Go 1.13.15 has a bug for package flag. Code below can help reproduce it.

config/init.go

package config

import "flag"
var mode string
func init() {

	flag.StringVar(&mode, "mode", "local", "go run main.go -mode 'local'")
	flag.Parse()
}

config/init_test.go

package config

import (
	"fmt"
	"testing"
)

func TestDefault(t *testing.T) {
	fmt.Println(mode)
}

output
go 1.12.17 ok

=== RUN   TestDefault
local
--- PASS: TestDefault (0.00s)
PASS

go 1.13.15

flag provided but not defined: -test.v
Usage of C:\Users\DELL\AppData\Local\Temp\___TestDefault_in_libgamedataapisrv_config.exe:
  -mode string
    	go run main.go -profPort ':6060' (default "local")

[the-moment]

still hava this in 1.16.3

[davecheney]

What is the exact command you ran?

[davecheney]

Sorry, you cannot call flag.Parse in init because it conflicts with the flags that are passed to the test binary. Move flag.parse to your main function

[agnivade]

What Dave said.

This is expected and documented: https://golang.org/doc/go1.13#testing, #31859.

Closing.

[the-moment]

What is the exact command you ran?

What Dave said.

This is expected and documented: https://golang.org/doc/go1.13#testing, #31859.

Closing.

I saw this question,but when will solve this problem.or should I notice that question in any program?

[the-moment]

What is the exact command you ran?

go test -v -run + myfun

[fwhezfwhez]

@the-moment
Write flag.Parse in main.go, whatever main.go init Func or main.go beginning. It's ok. And don't write flag.Parse in any init Func of other package.

By the way, testing function will auto call flag.Parse(). Style below is ok

package config

import "flag"
var mode string
func init() {
	flag.StringVar(&mode, "mode", "local", "go run main.go -mode 'local'")
}

package config

import (
	"fmt"
	"testing"
)

func TestDefault(t *testing.T) {
	fmt.Println(mode)
}

go test -run ^TestDefault$ -mode hehe

Output

hehe

As it suggests, hehe is output correctly even if I didn't call flag.Parse yet. It, flag.Parse, seems just called inside.

[davecheney]

Thats about it. Because flag.Parse operates on global state it must only be called once. The problem is both your package and, when compiled as a test, the testing package both define and parse flags, there is no way to make it work with flag.Parse called from init. Either:

• flag.Parse is called from your package, in which case the flags defined in the testing package haven't been defined yet so yo get a weird message about flags you didn't define causing the test process to fail.
• or, the testing package's flag.Parse is called and your flags aren't registered so your test blows up because the flags you were expecting aren't defined and cannot be used.

The root problem is the global flag.Parse singleton, but sadly that ship has long sailed. You can work around this by doing one or more of the following:

• Defining your own flag set
• calling flag.Parse in your main function, and no sooner.