go 1.9: New Helper() method in testing package does not work with testing.TB interface

[lukas....@googlemail.com]

I'm using helper functions in my test, for example this one:

// assert fails the test if the condition is false.
func assert(tb testing.TB, condition bool, msg string, v ...interface{}) {
 if !condition {
 _, file, line, _ := runtime.Caller(1)
 fmt.Printf("\033[31m%s:%d: "+msg+"\033[39m\n\n", append([]interface{}{filepath.Base(file), line}, v...)...)
 tb.FailNow()
 }
}

I hoped that I could improve these helpers with the new (*B).Helper() and (*T).Helper() methods:

// assert fails the test if the condition is false.

func assert(tb testing.TB, condition bool, msg string, v ...interface{}) {
tb.Helper()

if !condition {

tb.Fatalf("\033[31m "+msg+"\033[39m\n\n", v...)

}

}

I expected Go to print the file and line number of the failing test, followed by a red message. Instead, the file and line number is of form "<autogenerated>:1:"

It works if I replace tb testing.TB with t testing.T. Is there a reason the new Helper() method is part of the TB interface but not working as expected? Or could it be a bug?

[Caleb Spare]

Oh, shoot. It should be part of the interface. That was part of the proposal:

https://github.com/golang/proposal/blob/master/design/4899-testing-helper.md

but I forgot to add it.

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[Caleb Spare]

I filed https://github.com/golang/go/issues/21627. Thanks for the heads up.

[lukas....@googlemail.com]

It is part of the interface...

[Caleb Spare]

Yeah, sorry, I misread the report.

I can't reproduce the issue. Can you give a complete runnable example.

[lukas....@googlemail.com]

package bug

// Pow returns x raised to the power of y i.e. x^y.

func Pow(x, y int) int {

return x ^ y

}

package bug_test

import (

"fmt"

"testing"

"github.com/lukasmalkmus/bug"

)

func TestPow(t *testing.T) {

tests := []struct {

x, y, z int

}{

{0, 0, 0},

{1, 0, 1},

{0, 1, 11},

}

for _, tt := range tests {

t.Run("", func(t *testing.T) {

z := bug.Pow(tt.x, tt.y)

assert(t, tt.z == z, fmt.Sprintf("exp: %d, got: %d", tt.z, z))

})

}

}

// assert fails the test if the condition is false.

func assert(tb testing.TB, condition bool, msg string, v ...interface{}) {

tb.Helper()

if !condition {

tb.Fatalf("\033[31m "+msg+"\033[39m\n\n", v...)

}

}

This will error on test case 3.

I expected this output:

--- FAIL: TestPow (0.00s)

    --- FAIL: TestPow/#02 (0.00s)

    bug_test.go:22:  exp: 11, got: 1

    

FAIL

coverage: 100.0% of statements

exit status 1

FAIL github.com/lukasmalkmus/bug 0.008s

I got this:

--- FAIL: TestPow (0.00s)

    --- FAIL: TestPow/#02 (0.00s)

        <autogenerated>:1:  exp: 11, got: 1

    

FAIL

coverage: 100.0% of statements

FAIL    github.com/lukasmalkmus/bug     0.015s

Am Freitag, 25. August 2017 22:35:21 UTC+2 schrieb lukas....@googlemail.com:

[lukas....@googlemail.com]

I'm sorry, I think I made a huge mistake. The malicious output only occurs when running go test with the -race flag.

Am Freitag, 25. August 2017 22:35:21 UTC+2 schrieb lukas....@googlemail.com:

[Caleb Spare]

That's not a mistake. It's still a bug! Just doesn't seem like a very severe one. I filed https://github.com/golang/go/issues/21631.