proposal: testing: implement io.Writer with T and B

[poy]

Problem

Tests that have to create a *log.Logger do not (at least not out of the box) get to take advantage of testing's T.Log and the nice features that come with it.

This implies test writers have to either wrap T.Log up to make it implement io.Writer somehow and pass that into log.New(tlogger, "", 0), or discard their logs all together (e.g., log.New(ioutil.Discard, "", 0)).

Solution

Have testing.T and testing.B implement io.Writer.

This will allow developers to simply create a log.Logger by doing log.New(t, "", 0). It would also be compatible with most other logging libraries.

[dpinela]

I usually solve this the other way round:

type Logger interface {
  Log(args ...interface{})
}

type stdLogger struct {
  *log.Logger
}

func (s stdLogger) Log(args ...interface{}) { s.Println(args...) }

Then I log to the Logger interface, rather than to the *log.Logger directly.

[poy]

@dpinela That works as long as the developer has control over the interface. If however they are using a dependency that requires a *log.Logger, then that won't work for them.

[SamWhited]

For context, see the previous (rejected) proposal at https://golang.org/issues/22513 (#22513).

[rsc]

Line-at-a-time logging is not the same as a Write method (Writes are not guaranteed to be aligned with any useful boundary, certainly not lines). But this is not about Write at all. It's about log.Logger, which is/was #22513. Closing as duplicate.