testing/synctest: blocks forever when use time.Tick

[rschio]

Go version

1.24rc1

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=''
GOCACHE='/Users/rschio/Library/Caches/go-build'
GODEBUG=''
GOENV='/Users/rschio/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/rq/0fx96ptn7w5357fdm_qzflhh0000gn/T/go-build2099632737=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/private/tmp/learn_synctest/go.mod'
GOMODCACHE='/Users/rschio/go/pkg/mod'
GONOPROXY='github.com/rschio/*,buf.build/gen/go'
GONOSUMDB='github.com/rschio/*,buf.build/gen/go'
GOOS='darwin'
GOPATH='/Users/rschio/go'
GOPRIVATE='github.com/rschio/*,buf.build/gen/go'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/Users/rschio/go/pkg/mod/golang.org/[email protected]'
GOSUMDB='sum.golang.org'
GOTELEMETRY='on'
GOTELEMETRYDIR='/Users/rschio/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='go1.24rc1+auto'
GOTOOLDIR='/Users/rschio/go/pkg/mod/golang.org/[email protected]/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.24rc1'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

I was testing the new experimental package synctest with an adaptation of the code from https://danp.net/posts/synctest-experiment/ and observed that the test runs forever.

And I noticed that the commented code runs correctly (runs fast).

My code:
GOEXPERIMENT=synctest go test -v .

package main

import (
	"context"
	"sync/atomic"
	"testing"
	"testing/synctest"
	"time"
)

func Test(t *testing.T) {
	synctest.Run(func() {
		ctx := context.Background()
		ctx, cancel := context.WithCancel(ctx)

		var hits atomic.Int32
		go func() {
			t := time.Tick(time.Millisecond)
			//tick := time.NewTicker(time.Millisecond)
			//defer tick.Stop()
			for {
				select {
				case <-ctx.Done():
					return
				case <-t:
					//case <-tick.C:
					hits.Add(1)
				}
			}
		}()

		time.Sleep(4 * time.Millisecond)
		cancel()

		got := int(hits.Load())
		if want := 3; got != want {
			t.Fatalf("got %v, want %v", got, want)
		}
	})
}

What did you see happen?

The code provided runs forever or at least take too long.

What did you expect to see?

I expected to see the test complete in a reasonable time and I expected that time.NewTicker() to be equivalent to time.Tick() in the provided context.

[gabyhelp]

Related Issues

• testing/synctest: panic with `time.NewTimer` #70741 (closed)
• issue with time/tick #593 (closed)
• testing: "panic: Log in goroutine after Test..." is unreliable due to lack of synchronization on t.done #67701
• time: TestTicker timeouts after CL 232298 #42424 (closed)
• testing: inconsistent behaviors between running tests directly and after compiling the code first #59879 (closed)
• time: Ticker.Reset(0) deadlocks #49315 (closed)
• cmd/go: -test.timeout=0 does not cancel go tool's test timeout #18490 (closed)
• time: timer reset sometimes ignored, causing delayed ticks #47762 (closed)
• runtime: tests timing out #5025 (closed)
• testing: t.Fatal does not fatal tests if defers do not complete #22989 (closed)

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

[rschio]

Sorry I think this is a duplicate from #67434 (comment)