testing/synctest: inverted failure message in TestContextAfterFunc

[fgm]

Go version

go version go1.25.1 darwin/arm64

Output of go env in your module/workspace:

AR='ar'
CC='cc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='c++'
GCCGO='gccgo'
GO111MODULE=''
GOARCH='arm64'
GOARM64='v8.0'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/Users/fgm/Library/Caches/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/Users/fgm/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/by/bds0njgd56lcc5y_s3jxdqz40000gn/T/go-build37376917=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/Users/fgm/src/go/src/github.com/fgm/container/go.mod'
GOMODCACHE='/Users/fgm/src/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/fgm/src/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/opt/homebrew/Cellar/go/1.25.1/libexec'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/fgm/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/opt/homebrew/Cellar/go/1.25.1/libexec/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.25.1'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

Read the TestContextAfterFunc example and run it locally.

While running locally, comment out that synctest.Wait() calls to observe the failures.

What did you see happen?

The second test failure message in TestContextAfterFunc is incorrect. Here is the current code:

		// The context has not been canceled, so the AfterFunc is not called.
		synctest.Wait()
		if afterFuncCalled {
			t.Fatalf("before context is canceled: AfterFunc called")
		}

		// Cancel the context and wait for the AfterFunc to finish executing.
		// Verify that the AfterFunc ran.
		cancel()
		synctest.Wait()
		if !afterFuncCalled {
			t.Fatalf("before context is canceled: AfterFunc not called")
		}

The first message correctly reports failure if the function was called before the context was cancelled, but the second one correctly reports failure if the function was not called after the context was cancelled, but does so with an incorrect message, which should instead be "after context is canceled: AfterFunc not called" instead of before.

The smaller example in https://go.dev/blog/synctest does not have that problem:

cancel()

if !funcCalled() {
    t.Fatalf("AfterFunc function not called after context is canceled")
}

What did you expect to see?

after context is canceled: AfterFunc not called

[seankhliao]

feel free to send a CL

[gopherbot]

Change https://go.dev/cl/708275 mentions this issue: Issue #75685: inverted test failure message in TestContextAfterFunc

[cagedmantis]

@neild