testing: Helper line number has changed in 1.16

[ianlancetaylor]

This is the test program.

package main_test

import (
	"testing"
)

func TestHelper(t *testing.T) {
	helperA(t)
}

func helperA(t *testing.T) {
	t.Helper()

	t.Run("subtest", func(t *testing.T) {
		t.Helper()
		t.Fatal("fatal error message")
	})
}

When run using go test foo_test.go with Go 1.14 or Go 1.15, this program prints

--- FAIL: TestHelper (0.00s)
    --- FAIL: TestHelper/subtest (0.00s)
        foo_test.go:8: fatal error message
FAIL
FAIL	command-line-arguments	0.009s
FAIL

When run with Go 1.16 it prints

--- FAIL: TestHelper (0.00s)
    --- FAIL: TestHelper/subtest (0.00s)
        foo_test.go:14: fatal error message
FAIL
FAIL	command-line-arguments	0.007s
FAIL

The line number has changed from 8 to 14. Line number 14 is in a function that called t.Helper, so line 8 seems correct and line 14 seems wrong.

This appears to be due to https://golang.org/cl/231717. If I revert that CL, I see line number 8.

CC @bboreham

[ianlancetaylor]

@gopherbot Please open backport to 1.16

In some cases t.Helper seems to be ineffective. It's not critical but it's definitely annoying. We should fix it.

[gopherbot]

Backport issue(s) opened: #44888 (for 1.16).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://golang.org/wiki/MinorReleases.

[dnephin]

I just ran into this problem. I have been using a function runCase (see below) to make it easier to work with very large table tests. When a test spans thousands of lines it can be difficult to find the data for a specific failure. This runCase pattern has made it much easier to debug failing tests, and it no longer works due to this regression.

I notice this issue has been pushed out a couple patch releases. Please let me know if I can be of any help in restoring the old behaviour or testing a fix.

Example use case:

func runCase(t *testing.T, name string, fn func(t *testing.T)) {
	t.Helper()
	t.Run(name, func(t *testing.T) {
		t.Helper()
		t.Log("case:", name)
		fn(t)
	})
}

[gopherbot]

Change https://golang.org/cl/302469 mentions this issue: testing: fix Helper line number change

[gopherbot]

Change https://golang.org/cl/303189 mentions this issue: [release-branch.go1.16] testing: update helperNames just before checking it