testing: T and B should implement -ln methods

[cespare]

Like fmt and log, testing should provide -ln methods for T and B; that is, Errorln, Fatalln, Logln, and Skipln.

[davecheney]

Why ? Those methods already have an implicit line break appended, how would these new methods improve this ?

[cespare]

Same reasoning as for log.Println, log.Fatalln, etc.

I often write things like

log.Println("Updating foo bar in", baz)

or

log.Fatalln("Error while doing x y z:", err)

but when writing tests, I have to remember to use an alternate form:

t.Fatal("Cannot x y z: ", err)    // need space
t.Fatalf("Cannot x y z: %s", err) // need formatting code

[davecheney]

I think the latter are clearer, having to remember that the -ln version adds a space between the arguments, as well as trailing \n feels less clear to me.

[dominikh]

If one agreed with you, this would be "unfortunate". T.Fatal already exists, it cannot be removed or changed, and having an alias is worse than having just one slightly badly named function.

However, there's another point here: T.Fatal doesn't necessarily have to be understood as "print this fatal line". It's much rater a statement about the test (it ended fatally). It's not analogous to fmt or log.

[cespare]

@davecheney that argument seems to apply just as much to log.Println, log.Fatalln, etc. Would you have rather seen those functions removed prior to Go 1, or do you feel that there's some significant difference between log and the T/B methods?

I almost always want a space, so I use log.Println/Fatalln much more than I use log.Print/Fatal; this is why the lack of T.Errorln/Fatalln is noticeable to me.

[cespare]

@dominikh sure, one could view it that way.

I just filed this to register the fact that I've consistently felt that these are missing during a few years of writing Go tests. Even if unintentional, that's the impression I got after using the log and testing packages a bunch.

[bradfitz]

We can't extend the TB interface so I have a preference to not add common methods to T and B, so TB doesn't look lacking.

[dominikh]

@bradfitz TB contains unexported methods, so it should be possible to extend it?

[bradfitz]

Oh, pleasant surprise whenever evidence of past foresight is found.

[davecheney]

@davecheney that argument seems to apply just as much to log.Println, log.Fatalln, etc. Would you have rather seen those functions removed prior to Go 1, or do you feel that there's some significant difference between log and the T/B methods?

I don't have a position on those, we cannot change the past, but I don't see the argument for adding extra methods to testing to be compelling.

[davecheney]

Oh, pleasant surprise whenever evidence of past foresight is found.

eh ?

[adg]

@davecheney by "foresight" @bradfitz is referring to the private method in the interface, and its associated comment:

// TB is the interface common to T and B.
type TB interface {
    Error(args ...interface{})
    Errorf(format string, args ...interface{})
    Fail()
    FailNow()
    Failed() bool
    Fatal(args ...interface{})
    Fatalf(format string, args ...interface{})
    Log(args ...interface{})
    Logf(format string, args ...interface{})
    Skip(args ...interface{})
    SkipNow()
    Skipf(format string, args ...interface{})
    Skipped() bool

    // A private method to prevent users implementing the
    // interface and so future additions to it will not
    // violate Go 1 compatibility.
    private()
}

[davecheney]

That's a nice trick.

On Wed, 5 Aug 2015 08:49 Andrew Gerrand notifications@github.com wrote:

@davecheney https://github.com/davecheney by "foresight" @bradfitz
https://github.com/bradfitz is referring to the private method in the
interface, and its associated comment:

// TB is the interface common to T and B.
type TB interface {
Error(args ...interface{})
Errorf(format string, args ...interface{})
Fail()
FailNow()
Failed() bool
Fatal(args ...interface{})
Fatalf(format string, args ...interface{})
Log(args ...interface{})
Logf(format string, args ...interface{})
Skip(args ...interface{})
SkipNow()
Skipf(format string, args ...interface{})
Skipped() bool

// A private method to prevent users implementing the
// interface and so future additions to it will not
// violate Go 1 compatibility.
private()

}

—
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#12011 (comment).

[robpike]

For consistency with other printing things, this is probably a good thing to do although barely worthwhile.

[cespare]

I just noticed that t.Fatal and t.Error do insert the spaces between arguments (they call fmt.Sprintln), so this change doesn't make sense. It's still inconsistent with fmt/log, but it's probably too late to change now.

I'm not sure how I didn't notice this before, though. The code in question doesn't look like it has changed since 2011.