testing/slogtest: Parsing example fails when level is Error or Warn

[varun06]

What version of Go are you using (go version)?

$ go version
go version go1.21.0 darwin/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/Users/varun/Library/Caches/go-build'
GOENV='/Users/varun/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/varun/go/pkg/mod'
GONOPROXY='*.abc.com'
GONOSUMDB='*.abc.com'
GOOS='darwin'
GOPATH='/Users/varun/go'
GOPRIVATE='*.abc.com'
GOPROXY='direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/darwin_amd64'
GOVCS=''
GOVERSION='go1.21.0'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOMOD='/Users/varun/test/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/60/qpt9s9_s7lq9g9w7p53079nr0000gn/T/go-build3087313581=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

Copied example from package docs, added a level and tried running it.

func TestCustomHandler(t *testing.T) {
	var buf bytes.Buffer
	h := slog.NewJSONHandler(&buf, &slog.HandlerOptions{
		Level: slog.LevelError,
	})

	results := func() []map[string]any {
		var ms []map[string]any
		for _, line := range bytes.Split(buf.Bytes(), []byte{'\n'}) {
			if len(line) == 0 {
				continue
			}
			var m map[string]any
			if err := json.Unmarshal(line, &m); err != nil {
				t.Fatal(err)
			}
			ms = append(ms, m)
		}
		return ms
	}
	err := slogtest.TestHandler(h, results)
	if err != nil {
		t.Fatal(err)
	}
}

What did you expect to see?

I expected to see the test pass.

What did you see instead?

--- FAIL: TestCustomHandler (0.00s)
    /Users/varun/code/logger/multihandler_test.go:34: got 0 results, want 15

NOTE: Same test passes if Level is changed to Info or Debug.

[dmitshur]

CC @jba.

[seankhliao]

isn't this like #61706 (comment) where we don't expect it to pass?

[jba]

This is WAI. The slogtest package runs all its tests at Info level, so the logger must enable Info.

But the documentation could be improved.

[gopherbot]

Change https://go.dev/cl/520676 mentions this issue: testing/slogtest: clarify that passed handler must be enabled at info