Function Test_WithContextTemplateFailureOmitsPartialContext

log/default_test.go:278–304

Test_WithContextTemplateFailureOmitsPartialContext locks in the scratch-buffer guarantee from M8: a tag that writes some bytes before erroring must not leak its prefix into the real log line. Instead, the render-error marker stands in for the entire context block.

(t *testing.T)

// leak its prefix into the real log line. Instead, the render-error marker
// stands in for the entire context block.
func Test_WithContextTemplateFailureOmitsPartialContext(t *testing.T) {
	initDefaultLogger()

	templateErr := errors.New("template failure")
	require.NoError(t, SetContextTemplate(ContextConfig{
		Format: "[${broken}] ",
		CustomTags: map[string]ContextTagFunc{
			"broken": func(output Buffer, _ any, _ *ContextData, _ string) (int, error) {
				if _, err := output.WriteString("partial"); err != nil {
					return 0, err
				}
				return 0, templateErr
			},
		},
	}))
	t.Cleanup(func() { MustSetContextTemplate(ContextConfig{}) })

	var w byteSliceWriter
	SetOutput(&w)

	WithContext(context.Background()).Info("start")

	out := string(w.b)
	require.NotContains(t, out, "partial", "scratch buffer must isolate partial writes from the live log line")
	require.Contains(t, out, "ctx-render-error", "render error must be surfaced rather than silently dropped")
	require.Contains(t, out, "start", "log payload must still reach the writer")
}

func Test_LogfKeyAndValues(t *testing.T) {
	tests := []struct {