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testing: printing in tests without newline and running with -v -json omits a "run" action #72924

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Closed as duplicate
testing: printing in tests without newline and running with -v -json omits a "run" action#72924
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BugReportIssues describing a possible bug in the Go implementation.FrozenDueToAge

Description

@macabu
macabu
opened on Mar 18, 2025

Go version

go version go1.24.1 darwin/arm64

Output of go env in your module/workspace:

AR='ar'
CC='clang'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='clang++'
GCCGO='gccgo'
GO111MODULE=''
GOARCH='arm64'
GOARM64='v8.0'
GOAUTH='netrc'
GOBIN='/Users/macabu/go/bin'
GOCACHE='/Users/macabu/Library/Caches/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/Users/macabu/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/1j/6_mdph416630zgmq_7pl7j8m0000gn/T/go-build4105026236=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/Users/macabu/Projects/gotestcovjson/go.mod'
GOMODCACHE='/Users/macabu/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/macabu/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/nix/store/ja4jxx60lh1qfqfl4z4p2rff56ia1c3c-go-1.24.1/share/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/macabu/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/nix/store/ja4jxx60lh1qfqfl4z4p2rff56ia1c3c-go-1.24.1/share/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.24.1'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

With the following test file: https://go.dev/play/p/6WawLVaiaFW

package main

import (
	"fmt"
	"testing"
)

func Foo(v bool) {
	if v {
		fmt.Printf("value: %v", v)
	}
}

func TestFooSubTest(t *testing.T) {
	t.Run("true", func(t *testing.T) {
		Foo(true)
	})

	t.Run("false", func(t *testing.T) {
		Foo(false)
	})
}

What did you see happen?

Running:

go test -json ./...

Correctly outputs 3 run actions:

{"Time":"2025-03-18T17:08:10.054122+01:00","Action":"start","Package":"github.com/grafana/gotestcovjson"}
{"Time":"2025-03-18T17:08:10.054156+01:00","Action":"run","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest"}
{"Time":"2025-03-18T17:08:10.054158+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest","Output":"=== RUN   TestFooSubTest\n"}
{"Time":"2025-03-18T17:08:10.054162+01:00","Action":"run","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/true"}
{"Time":"2025-03-18T17:08:10.054163+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/true","Output":"=== RUN   TestFooSubTest/true\n"}
{"Time":"2025-03-18T17:08:10.054165+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/true","Output":"value: true"}
{"Time":"2025-03-18T17:08:10.05417+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/true","Output":"--- PASS: TestFooSubTest/true (0.00s)\n"}
{"Time":"2025-03-18T17:08:10.054183+01:00","Action":"pass","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/true","Elapsed":0}
{"Time":"2025-03-18T17:08:10.054186+01:00","Action":"run","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/false"}
{"Time":"2025-03-18T17:08:10.054187+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/false","Output":"=== RUN   TestFooSubTest/false\n"}
{"Time":"2025-03-18T17:08:10.054189+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/false","Output":"--- PASS: TestFooSubTest/false (0.00s)\n"}
{"Time":"2025-03-18T17:08:10.05419+01:00","Action":"pass","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/false","Elapsed":0}
{"Time":"2025-03-18T17:08:10.054191+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest","Output":"--- PASS: TestFooSubTest (0.00s)\n"}
{"Time":"2025-03-18T17:08:10.054195+01:00","Action":"pass","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest","Elapsed":0}
{"Time":"2025-03-18T17:08:10.054289+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Output":"PASS\n"}
{"Time":"2025-03-18T17:08:10.05429+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Output":"ok  \tgithub.com/grafana/gotestcovjson\t(cached)\n"}
{"Time":"2025-03-18T17:08:10.054294+01:00","Action":"pass","Package":"github.com/grafana/gotestcovjson","Elapsed":0}

While running:

go test -json -v ./...

Outputs 2 run actions, TestFooSubTest/false missing it:

{"Time":"2025-03-18T17:08:22.035856+01:00","Action":"start","Package":"github.com/grafana/gotestcovjson"}
{"Time":"2025-03-18T17:08:22.035892+01:00","Action":"run","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest"}
{"Time":"2025-03-18T17:08:22.035894+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest","Output":"=== RUN   TestFooSubTest\n"}
{"Time":"2025-03-18T17:08:22.035898+01:00","Action":"run","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/true"}
{"Time":"2025-03-18T17:08:22.0359+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/true","Output":"=== RUN   TestFooSubTest/true\n"}
{"Time":"2025-03-18T17:08:22.035903+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/true","Output":"value: true=== RUN   TestFooSubTest/false\n"}
{"Time":"2025-03-18T17:08:22.035906+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest","Output":"--- PASS: TestFooSubTest (0.00s)\n"}
{"Time":"2025-03-18T17:08:22.035919+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/true","Output":"    --- PASS: TestFooSubTest/true (0.00s)\n"}
{"Time":"2025-03-18T17:08:22.035921+01:00","Action":"pass","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/true","Elapsed":0}
{"Time":"2025-03-18T17:08:22.035925+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/false","Output":"    --- PASS: TestFooSubTest/false (0.00s)\n"}
{"Time":"2025-03-18T17:08:22.035929+01:00","Action":"pass","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/false","Elapsed":0}
{"Time":"2025-03-18T17:08:22.03593+01:00","Action":"pass","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest","Elapsed":0}
{"Time":"2025-03-18T17:08:22.035932+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Output":"PASS\n"}
{"Time":"2025-03-18T17:08:22.035933+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Output":"ok  \tgithub.com/grafana/gotestcovjson\t(cached)\n"}
{"Time":"2025-03-18T17:08:22.035998+01:00","Action":"pass","Package":"github.com/grafana/gotestcovjson","Elapsed":0}

If you tweak the Foo function to print with a newline \n:

func Foo(v bool) {
	if v {
		fmt.Printf("value: %v\n", v)
	}
}

And re-run with:

go test -json -v ./...

It outputs the expected 3 run actions:

{"Time":"2025-03-18T17:09:39.595521+01:00","Action":"start","Package":"github.com/grafana/gotestcovjson"}
{"Time":"2025-03-18T17:09:39.595571+01:00","Action":"run","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest"}
{"Time":"2025-03-18T17:09:39.595574+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest","Output":"=== RUN   TestFooSubTest\n"}
{"Time":"2025-03-18T17:09:39.595577+01:00","Action":"run","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/true"}
{"Time":"2025-03-18T17:09:39.59558+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/true","Output":"=== RUN   TestFooSubTest/true\n"}
{"Time":"2025-03-18T17:09:39.595585+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/true","Output":"value: true\n"}
{"Time":"2025-03-18T17:09:39.59559+01:00","Action":"run","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/false"}
{"Time":"2025-03-18T17:09:39.595592+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/false","Output":"=== RUN   TestFooSubTest/false\n"}
{"Time":"2025-03-18T17:09:39.5956+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest","Output":"--- PASS: TestFooSubTest (0.00s)\n"}
{"Time":"2025-03-18T17:09:39.595602+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/true","Output":"    --- PASS: TestFooSubTest/true (0.00s)\n"}
{"Time":"2025-03-18T17:09:39.595603+01:00","Action":"pass","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/true","Elapsed":0}
{"Time":"2025-03-18T17:09:39.595605+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/false","Output":"    --- PASS: TestFooSubTest/false (0.00s)\n"}
{"Time":"2025-03-18T17:09:39.595609+01:00","Action":"pass","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest/false","Elapsed":0}
{"Time":"2025-03-18T17:09:39.595681+01:00","Action":"pass","Package":"github.com/grafana/gotestcovjson","Test":"TestFooSubTest","Elapsed":0}
{"Time":"2025-03-18T17:09:39.595682+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Output":"PASS\n"}
{"Time":"2025-03-18T17:09:39.595683+01:00","Action":"output","Package":"github.com/grafana/gotestcovjson","Output":"ok  \tgithub.com/grafana/gotestcovjson\t(cached)\n"}
{"Time":"2025-03-18T17:09:39.595689+01:00","Action":"pass","Package":"github.com/grafana/gotestcovjson","Elapsed":0}

What did you expect to see?

The output json to contain 3 run actions in all cases.

Activity

  1. ianlancetaylor commented on Mar 18, 2025

    @ianlancetaylor
    ianlancetaylor
    on Mar 18, 2025
    Contributor

    Probably related to the issues discussed in #38063.

  2. ianlancetaylor
    changed the title [-]go test: printing in tests without newline and running with -v -json omits a "run" action[/-] [+]testing: printing in tests without newline and running with -v -json omits a "run" action[/+] on Mar 18, 2025

  3. macabu commented on Mar 18, 2025

    @macabu
    macabu
    on Mar 18, 2025
    Author

    Thanks! We will use the workaround of adding \n

    Perhaps this one can be closed then as duplicate of the one mentioned.

  4. gabyhelp commented on Mar 18, 2025

    @gabyhelp
    gabyhelp
    on Mar 18, 2025

    Related Issues

    (Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)

  5. gabyhelp
    added
    BugReportIssues describing a possible bug in the Go implementation.
    on Mar 18, 2025
  6. macabu
    closed this as duplicateon Mar 18, 2025
  7. golang
    locked and limited conversation to collaborators on Mar 18, 2026
  8. gopherbot
    added
    FrozenDueToAge
    on Mar 18, 2026
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