Logrus: while testing, redirect output to testing.T

[drewwells]

The testing package has many logging functions that are used for logging only when errors are encountered. It would be beneficial to be able to easily redirect output to this. I can't see a simple way to do this currently besides creating an io.Writer that outputs to testing.Logf.

[dgsb]

Hi @drewwells, I've you tried somehow to set the logger.Out field to os.Stdout instead of os.Stderr ? I wonder if the test environment doesn't do something Stdout in order to only have its output upon test failure.

[pkqk]

@drewwells it's slightly tricky since you need to get access to the *testing.T instance of each test, and it is hardcoded to look back a certain number of stack frames for the calling location.

In one of our projects at work we have this:

package serenity

import (
    "io"
    "os"
    "testing"
    "github.com/sirupsen/logrus"
)

// LogCapturer reroutes testing.T log output
type LogCapturer interface {
    Release()
}

type logCapturer struct {
    *testing.T
    origOut io.Writer
}

func (tl logCapturer) Write(p []byte) (n int, err error) {
    tl.Logf((string)(p))
    return len(p), nil
}

func (tl logCapturer) Release() {
    logrus.SetOutput(tl.origOut)
}

// CaptureLog redirects logrus output to testing.Log
func CaptureLog(t *testing.T) LogCapturer {
    lc := logCapturer{T: t, origOut: logrus.StandardLogger().Out}
    if !testing.Verbose() {
        logrus.SetOutput(lc)
    }
    return &lc
}

But it does mean in every test you need to do:
```golang
func TestFoo(t *testing.T) {
defer serenity.CaptureLog(t).Release()
…
}

[adamcavendish]

We can use logrus.SetOutput(ioutil.Discard) to disable output.

import (
    "io/ioutil"
        "testing"
    "github.com/sirupsen/logrus"
)

func TestFoo(t *testing.T) {
    logrus.Info("Logrus in Testing")
}

func TestMain(m *testing.M) {
    logrus.SetOutput(ioutil.Discard)
    os.Exit(m.Run())
}

Note: we need to call m.Run() to execute the test after defining the TestMain.