Use the -v flag to get verbose output from Go tests

This prints all t.Log and t.Logf calls, even if the test succeeds or times out.

I had a Go test which was timing out, and I wanted to see the log messages being written by t.Log and t.Logf to find out where it was getting stuck. Normally these messages are only written if the test fails, to help you with debugging.

Unfortunately, if you run go test with the -timeout flag and the test exceeds the timeout, Go panics and the test immediately ends. None of the log messages get printed, the test just fails.

Running go test with the -v flag (verbose) means it prints log messages immediately, so they aren’t lost if the test panics.

Example

Here’s an example of a test which prints a bunch of logs, and has a long hang halfway through:

package chatty

import (
	"testing"
	"time"
)

func TestChatty(t *testing.T) {
	t.Log("starting the test")
	for i := range 5 {
		if i == 4 {
			time.Sleep(10 * time.Second)
		}
		t.Logf("running test case %d", i)
	}
	t.Log("finishing the test")
}

Here’s the output of different go test commands, slightly elided for readability:

$ go test chatty_test.go
ok  	command-line-arguments	10.142s

$ go test -v chatty_test.go
=== RUN   TestChatty
    chatty_test.go:9: starting the test
    chatty_test.go:14: running test case 0
    chatty_test.go:14: running test case 1
    chatty_test.go:14: running test case 2
    chatty_test.go:14: running test case 3
    chatty_test.go:14: running test case 4
    chatty_test.go:16: finishing the test
--- PASS: TestChatty (10.00s)
PASS
ok  	command-line-arguments	10.141s

$ go test -timeout 1s chatty_test.go
panic: test timed out after 1s
	running tests:
		TestChatty (1s)

goroutine 4 [running]:
testing.(*M).startAlarm.func1()
  […]

goroutine 1 [chan receive]:
testing.(*T).Run(0x14000002fc0, {0x100abf8d5?, 0x1400007ab38?}, 0x100b36560)
  […]

goroutine 3 [sleep]:
time.Sleep(0x2540be400)
  […]
FAIL	command-line-arguments	1.140s
FAIL

$ go test -v -timeout 1s chatty_test.go
=== RUN   TestChatty
    chatty_test.go:9: starting the test
    chatty_test.go:14: running test case 0
    chatty_test.go:14: running test case 1
    chatty_test.go:14: running test case 2
    chatty_test.go:14: running test case 3
panic: test timed out after 1s
	running tests:
		TestChatty (1s)

goroutine 35 [running]:
testing.(*M).startAlarm.func1()
  […]

goroutine 1 [chan receive]:
  […]

goroutine 34 [sleep]:
  […]
FAIL	command-line-arguments	1.141s
FAIL

When the test times out, adding the -v flag gives us more information about where the test got stuck.