testing: Benchmark doesn't collect result of sub-benchmarks

[uvelichitel]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

1.7.4
go version devel +78860b2ad

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build805050938=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"

What did you do?

I run program normal way, not "go test". I call testing.Benchmark() in code. Benchmark function call Run() method to execute sub benchmark.

func main() {
    result := testing.Benchmark(func(parentB *testing.B) {
        parentB.Run("example", func(b *testing.B) {
            for n := 0; n < b.N; n++ {
                println("ok")
            }
        })
    })
    println(result.String())
}

Behaviour already reproduced prooflink http://stackoverflow.com/questions/41861918/using-testing-benchmark-does-not-produce-any-output

What did you expect to see?

According to the documentation I expect

Benchmark benchmarks a single function. Useful for creating custom benchmarks that do not use the "go test" command.

If f calls Run, the result will be an estimate of running all its subbenchmarks that don't call Run in sequence in a single benchmark.

What did you see instead?

Sub benchmark run N times(no once) but result is
0 0 ns/op

[ianlancetaylor]

I think the bug is that Benchmark returns an empty BenchmarkResult if b.run1() returns false. It should return b.result.

[robpike]

There may be a but as @ianlancetaylor says, but I would still not expect the testing package to work properly unless the program is run with go test. The go test command sets up the environment for the test and benchmarks. The go run command does not.

[uvelichitel]

b.run1() seems to return true. Sub - benchmark is evaluated N times, no once, checked with debug prints. RunParallel() works as expected in same circumstances.

[cespare]

@robpike I always thought this was an intended and documented use case for the testing package. Otherwise, what is the purpose of the Benchmark function?

func Benchmark(f func(b *B)) BenchmarkResult
    Benchmark benchmarks a single function. Useful for creating custom
    benchmarks that do not use the "go test" command.

    If f calls Run, the result will be an estimate of running all its
    subbenchmarks that don't call Run in sequence in a single benchmark.

[robpike]

The purpose of the Benchmark function is to run a benchmark under the auspices of "go test".
I'm not saying it mustn't work outside of "go test", just that it wouldn't surprise me if it didn't.

Here is the start of the package docs:

Package testing provides support for automated testing of Go packages. It is
intended to be used in concert with the ``go test'' command, which automates
execution of any function of the form ...

[mpvl]

I agree this is a bug. Like Ian said, it should still return b.result.

[gopherbot]

CL https://golang.org/cl/36990 mentions this issue.