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testing: Benchmark prints nothing on failure #32066

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rogpeppe opened this issue May 15, 2019 · 3 comments
Open

testing: Benchmark prints nothing on failure #32066

rogpeppe opened this issue May 15, 2019 · 3 comments
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NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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Backlog

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@rogpeppe
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Benchmark functions can call Log, Error and Fatal, but if the benchmark is run with the Benchmark function, all messages are discarded.

https://play.golang.org/p/fd5Ed-il70V

Perhaps the messages should be printed to standard error?
@josharian josharian changed the title Benchmark prints nothing on failure testing: Benchmark prints nothing on failure May 15, 2019
@FiloSottile FiloSottile added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label May 16, 2019
@FiloSottile FiloSottile added this to the Go1.14 milestone May 16, 2019
@fodil-a
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fodil-a commented May 20, 2019 •
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Hi, I can confirm that the output is discarded, here is the writer used in the context of the benchmark

go/src/testing/benchmark.go

Line 772 in fbc6a97

w: discard{},

Calls from Log, Error, or Fatal will print nothing, because the Write call of the discard writer does nothing.

go/src/testing/benchmark.go

Lines 783 to 785 in fbc6a97

type discard struct{}
func (discard) Write(b []byte) (n int, err error) { return len(b), nil }

@rsc rsc modified the milestones: Go1.14, Backlog Oct 9, 2019
@lahsivjar
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I stumbled upon this today, any updates on this? It feels like a pretty valid case and I was hoping it could do one of the following:

  1. testing.Benchmark takes io.Writer as an input.
  2. Allow users to create a custom testing.B and call Benchmark on top of it.

@fodil-a
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fodil-a commented Aug 22, 2023

If anyone from the team agrees the the approach of creating a new func that take a io.Writer and uses it here

go/src/testing/benchmark.go

Line 772 in fbc6a97

w: discard{},

I can do the code, should be pretty easy to add and test 😊

@constanca-m constanca-m mentioned this issue Feb 27, 2025
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@carsonip carsonip mentioned this issue Mar 3, 2025
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@rogpeppe @rsc @FiloSottile @lahsivjar @fodil-a