Test explorer about 25 times slower with many subtests

What version of Go, VS Code & VS Code Go extension are you using?

Version Information

* Run `go version` to get version of Go from _the VS Code integrated terminal_. - go version go1.22.3 darwin/arm64 * Run `gopls -v version` to get version of Gopls from _the VS Code integrated terminal_. ``` Build info ---------- golang.org/x/tools/gopls v0.15.3 golang.org/x/tools/gopls@v0.15.3 h1:zbdOidFrPTc8Bx0YrN5QKgJ0zCjyGi0L27sKQ/bDG5o= github.com/BurntSushi/toml@v1.2.1 h1:9F2/+DoOYIOksmaJFPw1tGFy1eDnIJXg+UHjuD8lTak= github.com/google/go-cmp@v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI= golang.org/x/exp/typeparams@v0.0.0-20221212164502-fae10dda9338 h1:2O2DON6y3XMJiQRAS1UWU+54aec2uopH3x7MAiqGW6Y= golang.org/x/mod@v0.15.0 h1:SernR4v+D55NyBH2QiEQrlBAnj1ECL6AGrA5+dPaMY8= golang.org/x/sync@v0.6.0 h1:5BMeUDZ7vkXGfEr1x9B4bRcTH4lpkTkpdh0T/J+qjbQ= golang.org/x/telemetry@v0.0.0-20240209200032-7b892fcb8a78 h1:vcVnuftN4J4UKLRcgetjzfU9FjjgXUUYUc3JhFplgV4= golang.org/x/text@v0.14.0 h1:ScX5w1eTa3QqT8oi6+ziP7dTV1S2+ALU0bI+0zXKWiQ= golang.org/x/tools@v0.18.1-0.20240412183611-d92ae0781217 h1:uH9jJYgeLCvblH0S+03kFO0qUDxRkbLRLFiKVVDl7ak= golang.org/x/vuln@v1.0.1 h1:KUas02EjQK5LTuIx1OylBQdKKZ9jeugs+HiqO5HormU= honnef.co/go/tools@v0.4.6 h1:oFEHCKeID7to/3autwsWfnuv69j3NsfcXbvJKuIcep8= mvdan.cc/gofumpt@v0.6.0 h1:G3QvahNDmpD+Aek/bNOLrFR2XC6ZAdo62dZu65gmwGo= mvdan.cc/xurls/v2@v2.5.0 h1:lyBNOm8Wo71UknhUs4QTFUNNMyxy2JEIaKKo0RWOh+8= go: devel go1.23-890179d949 Thu Apr 11 17:09:10 2024 +0000 X:rangefunc ``` * Run `code -v` or `code-insiders -v` to get version of VS Code or VS Code Insiders. - Version: 1.89.0 (Universal) * Check your installed extensions to get the version of the VS Code Go extension - v0.41.4 * Run Ctrl+Shift+P (Cmd+Shift+P on Mac OS) > `Go: Locate Configured Go Tools` command. ``` # Tools Configuration ## Environment GOBIN: undefined toolsGopath: gopath: /Users/flo/go GOROOT: /Users/flo/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.22.0.darwin-arm64 PATH: /opt/homebrew/bin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/Applications/Wireshark.app/Contents/MacOS ## Tools go: /opt/homebrew/bin/go: go version go1.22.0 darwin/arm64 gopls: /Users/flo/go/bin/gopls (version: v0.15.3 built with go: go1.23-890179d949) gotests: /Users/flo/go/bin/gotests (version: v1.6.0 built with go: go1.23-4a7f3ac8) gomodifytags: /Users/flo/go/bin/gomodifytags (version: v1.16.0 built with go: go1.23-4a7f3ac8) impl: /Users/flo/go/bin/impl (version: v1.1.0 built with go: go1.23-4a7f3ac8) goplay: /Users/flo/go/bin/goplay (version: v1.0.0 built with go: go1.23-4a7f3ac8) dlv: /Users/flo/go/bin/dlv (version: v1.22.1 built with go: go1.21.1) ## Go env Workspace Folder (vccode_test_slowness_repo): /Users/flo/Projects/go/vccode_test_slowness_repo GO111MODULE='' GOARCH='arm64' GOBIN='' GOCACHE='/Users/flo/Library/Caches/go-build' GOENV='/Users/flo/Library/Application Support/go/env' GOEXE='' GOEXPERIMENT='' GOFLAGS='' GOHOSTARCH='arm64' GOHOSTOS='darwin' GOINSECURE='' GOMODCACHE='/Users/flo/go/pkg/mod' GONOPROXY='*.home.znkr.io' GONOSUMDB='*.home.znkr.io' GOOS='darwin' GOPATH='/Users/flo/go' GOPRIVATE='*.home.znkr.io' GOPROXY='https://proxy.golang.org,direct' GOROOT='/Users/flo/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.22.3.darwin-arm64' GOSUMDB='sum.golang.org' GOTMPDIR='' GOTOOLCHAIN='auto' GOTOOLDIR='/Users/flo/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.22.3.darwin-arm64/pkg/tool/darwin_arm64' GOVCS='' GOVERSION='go1.22.3' GCCGO='gccgo' AR='ar' CC='clang' CXX='clang++' CGO_ENABLED='1' GOMOD='/Users/flo/Projects/go/vccode_test_slowness_repo/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 arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/1_/dsgxrj_j2ws_5h4ykmddqjyr0000gn/T/go-build2964250531=/tmp/go-build -gno-record-gcc-switches -fno-common' ```

Share the Go related settings you have added/edited

    "go.coverageDecorator": {
        "type": "gutter",
        "coveredHighlightColor": "rgba(64,128,128,0.5)",
        "uncoveredHighlightColor": "rgba(128,64,64,0.25)",
        "coveredBorderColor": "rgba(64,128,128,0.5)",
        "uncoveredBorderColor": "rgba(128,64,64,0.25)",
        "coveredGutterStyle": "blockblue",
        "uncoveredGutterStyle": "slashyellow"
    },
    "go.coverOnSingleTest": true,
    "go.coverOnSingleTestFile": true,
    "go.coverOnSave": true,
    "go.testOnSave": true,
    "go.testExplorer.showDynamicSubtestsInEditor": true,
    "go.testExplorer.showOutput": false,

Describe the bug

I have a project that includes thousands of tests, most of these are generated from testdata files. When I use the test explorer to run the tests it takes significantly longer to run these tests than when I run go test ./... directly. At first I thought that this might be due to caching, but turned out to be false. Even with all caches cleared, the test explorer is still a lot slower.

I recently showed the issue to @hyangah and we agreed that I file an issue here.

Steps to reproduce the behavior:

Create a new project with a test file containing

func Test(t *testing.T) {
    for i := range 1000 {
        t.Run(fmt.Sprintf("test_%03d", i), func(t *testing.T) {
            // intentionally left empty
        })
    }
}

Click on "Run Tests" in the test explorer to run all tests
Run go test manually
On my machine (M1 Macbook), the test explorer run takes about 5 seconds while the go test run takes about 0.2 seconds. I would expect that both are about the same.

golang / vscode-go