Repository: go
Issue: x/net/http2: several benchmarks crash
Labels: NeedsInvestigation

### Go version

go version go1.22.8 darwin/amd64

### Output of `go env` in your module/workspace:

```shell
GO111MODULE='auto'
GOARCH='amd64'
GOBIN=''
GOCACHE='/tmp/.gocache'
GOENV='/Users/rittneje/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/rittneje/go/pkg/mod'
GONOPROXY='[REDACTED]'
GONOSUMDB='[REDACTED]'
GOOS='darwin'
GOPATH='/Users/rittneje/go'
GOPRIVATE='[REDACTED]'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/Users/rittneje/go1.22.8'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='local'
GOTOOLDIR='/Users/rittneje/go1.22.8/pkg/tool/darwin_amd64'
GOVCS='[REDACTED]'
GOVERSION='go1.22.8'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOMOD='/Users/rittneje/golang.org_x_net/go.mod'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/kf/kr7_s3xx0l12zbj3jrn082hmzy5gvy/T/go-build1111184570=/tmp/go-build -gno-record-gcc-switches -fno-common'
```


### What did you do?

Tried to run any benchmark from golang.org/x/net/http2 that uses `newServerTesterWithRealConn`.
1. `BenchmarkServerGets`
2. `BenchmarkServerPosts`
3. `BenchmarkServerToClientStreamDefaultOptions`
4. `BenchmarkServerToClientStreamReuseFrames`
5. `BenchmarkServer_GetRequest`
6. `BenchmarkServer_PostRequest`

### What did you see happen?

They all crash, because `newServerTesterWithRealConn` neglects to initialize the `serverTester`'s `group` field.

```
$ go test -run=^$ -bench=BenchmarkServerGets ./http2
goos: darwin
goarch: amd64
pkg: golang.org/x/net/http2
cpu: Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0xd4c36c7]

goroutine 28 [running]:
golang.org/x/net/http2.(*synctestGroup).idle(0x0)
        /Users/rittneje/golang.org_x_net/http2/sync_test.go:84 +0x47
golang.org/x/net/http2.(*synctestGroup).Wait(0x0)
        /Users/rittneje/golang.org_x_net/http2/sync_test.go:75 +0x2f
golang.org/x/net/http2.(*serverTester).sync(...)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:336
golang.org/x/net/http2.(*serverTester).greetAndCheckSettings(0xc0001703c0, 0xd66f888)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:440 +0x85
golang.org/x/net/http2.(*serverTester).greet(0xc0001703c0)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:433 +0x35
golang.org/x/net/http2.BenchmarkServerGets(0xc000166c88)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:2884 +0xae
testing.(*B).runN(0xc000166c88, 0x1)
        /Users/rittneje/go1.22.8/src/testing/benchmark.go:193 +0xf8
testing.(*B).run1.func1()
        /Users/rittneje/go1.22.8/src/testing/benchmark.go:215 +0x4e
created by testing.(*B).run1 in goroutine 1
        /Users/rittneje/go1.22.8/src/testing/benchmark.go:208 +0x90
exit status 2
FAIL    golang.org/x/net/http2  0.672s
FAIL
```

```
$ go test -run=^$ -bench=BenchmarkServerPosts ./http2
goos: darwin
goarch: amd64
pkg: golang.org/x/net/http2
cpu: Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
BenchmarkServerPosts-16         panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x18ea6c7]

goroutine 5 [running]:
golang.org/x/net/http2.(*synctestGroup).idle(0x0)
        /Users/rittneje/golang.org_x_net/http2/sync_test.go:84 +0x47
golang.org/x/net/http2.(*synctestGroup).Wait(0x0)
        /Users/rittneje/golang.org_x_net/http2/sync_test.go:75 +0x2f
golang.org/x/net/http2.(*serverTester).sync(...)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:336
golang.org/x/net/http2.(*serverTester).greetAndCheckSettings(0xc0001703c0, 0x1a96888)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:440 +0x85
golang.org/x/net/http2.(*serverTester).greet(0xc0001703c0)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:433 +0x35
golang.org/x/net/http2.BenchmarkServerPosts(0xc000166c88)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:2926 +0xeb
testing.(*B).runN(0xc000166c88, 0x1)
        /Users/rittneje/go1.22.8/src/testing/benchmark.go:193 +0xf8
testing.(*B).run1.func1()
        /Users/rittneje/go1.22.8/src/testing/benchmark.go:215 +0x4e
created by testing.(*B).run1 in goroutine 1
        /Users/rittneje/go1.22.8/src/testing/benchmark.go:208 +0x90
exit status 2
FAIL    golang.org/x/net/http2  0.287s
FAIL
```

```
$ go test -run=^$ -bench=BenchmarkServer_GetRequest ./http2
goos: darwin
goarch: amd64
pkg: golang.org/x/net/http2
cpu: Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
BenchmarkServer_GetRequest-16           panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0xd58c6c7]

goroutine 12 [running]:
golang.org/x/net/http2.(*synctestGroup).idle(0x0)
        /Users/rittneje/golang.org_x_net/http2/sync_test.go:84 +0x47
golang.org/x/net/http2.(*synctestGroup).Wait(0x0)
        /Users/rittneje/golang.org_x_net/http2/sync_test.go:75 +0x2f
golang.org/x/net/http2.(*serverTester).sync(...)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:336
golang.org/x/net/http2.(*serverTester).greetAndCheckSettings(0xc0000f63c0, 0xd738888)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:440 +0x85
golang.org/x/net/http2.(*serverTester).greet(0xc0000f63c0)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:433 +0x35
golang.org/x/net/http2.BenchmarkServer_GetRequest(0xc0000eec88)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:3278 +0xeb
testing.(*B).runN(0xc0000eec88, 0x1)
        /Users/rittneje/go1.22.8/src/testing/benchmark.go:193 +0xf8
testing.(*B).run1.func1()
        /Users/rittneje/go1.22.8/src/testing/benchmark.go:215 +0x4e
created by testing.(*B).run1 in goroutine 1
        /Users/rittneje/go1.22.8/src/testing/benchmark.go:208 +0x90
exit status 2
FAIL    golang.org/x/net/http2  0.300s
FAIL
```

```
$ go test -run=^$ -bench=BenchmarkServer_PostRequest ./http2
goos: darwin
goarch: amd64
pkg: golang.org/x/net/http2
cpu: Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
BenchmarkServer_PostRequest-16          panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x5f4d6c7]

goroutine 26 [running]:
golang.org/x/net/http2.(*synctestGroup).idle(0x0)
        /Users/rittneje/golang.org_x_net/http2/sync_test.go:84 +0x47
golang.org/x/net/http2.(*synctestGroup).Wait(0x0)
        /Users/rittneje/golang.org_x_net/http2/sync_test.go:75 +0x2f
golang.org/x/net/http2.(*serverTester).sync(...)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:336
golang.org/x/net/http2.(*serverTester).greetAndCheckSettings(0xc0001703c0, 0x60f9888)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:440 +0x85
golang.org/x/net/http2.(*serverTester).greet(0xc0001703c0)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:433 +0x35
golang.org/x/net/http2.BenchmarkServer_PostRequest(0xc000166c88)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:3315 +0xeb
testing.(*B).runN(0xc000166c88, 0x1)
        /Users/rittneje/go1.22.8/src/testing/benchmark.go:193 +0xf8
testing.(*B).run1.func1()
        /Users/rittneje/go1.22.8/src/testing/benchmark.go:215 +0x4e
created by testing.(*B).run1 in goroutine 1
        /Users/rittneje/go1.22.8/src/testing/benchmark.go:208 +0x90
exit status 2
FAIL    golang.org/x/net/http2  0.304s
FAIL
```

```
$ go test -run=^$ -bench=BenchmarkServerToClientStreamDefaultOptions ./http2
goos: darwin
goarch: amd64
pkg: golang.org/x/net/http2
cpu: Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
BenchmarkServerToClientStreamDefaultOptions-16          panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x228d6c7]

goroutine 50 [running]:
golang.org/x/net/http2.(*synctestGroup).idle(0x0)
        /Users/rittneje/golang.org_x_net/http2/sync_test.go:84 +0x47
golang.org/x/net/http2.(*synctestGroup).Wait(0x0)
        /Users/rittneje/golang.org_x_net/http2/sync_test.go:75 +0x2f
golang.org/x/net/http2.(*serverTester).sync(...)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:336
golang.org/x/net/http2.(*serverTester).greetAndCheckSettings(0xc0001e83c0, 0x2439888)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:440 +0x85
golang.org/x/net/http2.(*serverTester).greet(0xc0001e83c0)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:433 +0x35
golang.org/x/net/http2.benchmarkServerToClientStream(0xc0001dec88, {0x0, 0x0, 0x0})
        /Users/rittneje/golang.org_x_net/http2/server_test.go:2997 +0x11c
golang.org/x/net/http2.BenchmarkServerToClientStreamDefaultOptions(0xc0001dec88?)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:2958 +0x1a
testing.(*B).runN(0xc0001dec88, 0x1)
        /Users/rittneje/go1.22.8/src/testing/benchmark.go:193 +0xf8
testing.(*B).run1.func1()
        /Users/rittneje/go1.22.8/src/testing/benchmark.go:215 +0x4e
created by testing.(*B).run1 in goroutine 1
        /Users/rittneje/go1.22.8/src/testing/benchmark.go:208 +0x90
exit status 2
FAIL    golang.org/x/net/http2  0.316s
FAIL
```

```
$ go test -run=^$ -bench=BenchmarkServerToClientStreamReuseFrames ./http2
goos: darwin
goarch: amd64
pkg: golang.org/x/net/http2
cpu: Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
BenchmarkServerToClientStreamReuseFrames-16     panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0xe1016c7]

goroutine 14 [running]:
golang.org/x/net/http2.(*synctestGroup).idle(0x0)
        /Users/rittneje/golang.org_x_net/http2/sync_test.go:84 +0x47
golang.org/x/net/http2.(*synctestGroup).Wait(0x0)
        /Users/rittneje/golang.org_x_net/http2/sync_test.go:75 +0x2f
golang.org/x/net/http2.(*serverTester).sync(...)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:336
golang.org/x/net/http2.(*serverTester).greetAndCheckSettings(0xc0000f63c0, 0xe2ad888)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:440 +0x85
golang.org/x/net/http2.(*serverTester).greet(0xc0000f63c0)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:433 +0x35
golang.org/x/net/http2.benchmarkServerToClientStream(0xc0000eec88, {0xc000093f30, 0x1, 0x1})
        /Users/rittneje/golang.org_x_net/http2/server_test.go:2997 +0x11c
golang.org/x/net/http2.BenchmarkServerToClientStreamReuseFrames(0xc0000eec88)
        /Users/rittneje/golang.org_x_net/http2/server_test.go:2964 +0x57
testing.(*B).runN(0xc0000eec88, 0x1)
        /Users/rittneje/go1.22.8/src/testing/benchmark.go:193 +0xf8
testing.(*B).run1.func1()
        /Users/rittneje/go1.22.8/src/testing/benchmark.go:215 +0x4e
created by testing.(*B).run1 in goroutine 1
        /Users/rittneje/go1.22.8/src/testing/benchmark.go:208 +0x90
exit status 2
FAIL    golang.org/x/net/http2  0.316s
FAIL
```

### What did you expect to see?

They should all work, or be removed.