Ensure jsonfile is flushed before running post-run-command

The test seems to pass without these extra Flush, but from what I can
tell there's no guarantee the file is sycned to disk without these
new calls.

cmd/handler.go

@@ -15,10 +15,15 @@ import (
 type eventHandler struct {
 	formatter testjson.EventFormatter
 	err       io.Writer
-	jsonFile  io.WriteCloser
+	jsonFile  writeSyncer
 	maxFails  int
 }
 
+type writeSyncer interface {
+	io.WriteCloser
+	Sync() error
+}
+
 func (h *eventHandler) Err(text string) error {
 	_, _ = h.err.Write([]byte(text + "\n"))
 	// always return nil, no need to stop scanning if the stderr write fails
@@ -45,6 +50,14 @@ func (h *eventHandler) Event(event testjson.TestEvent, execution *testjson.Execu
 	return nil
 }
 
+func (h *eventHandler) Flush() {
+	if h.jsonFile != nil {
+		if err := h.jsonFile.Sync(); err != nil {
+			log.Errorf("Failed to sync JSON file: %v", err)
+		}
+	}
+}
+
 func (h *eventHandler) Close() error {
 	if h.jsonFile != nil {
 		if err := h.jsonFile.Close(); err != nil {
@@ -118,6 +131,5 @@ func postRunHook(opts *options, execution *testjson.Execution) error {
 		fmt.Sprintf("TESTS_SKIPPED=%d", len(execution.Skipped())),
 		fmt.Sprintf("TESTS_ERRORS=%d", len(execution.Errors())),
 	)
-	// TODO: send a more detailed report to stdin?
 	return cmd.Run()
 }

cmd/handler_test.go

@@ -56,6 +56,8 @@ type bufferCloser struct {
 
 func (bufferCloser) Close() error { return nil }
 
+func (bufferCloser) Sync() error { return nil }
+
 func TestEventHandler_Event_WithMissingActionFail(t *testing.T) {
 	buf := new(bufferCloser)
 	errBuf := new(bytes.Buffer)

cmd/main.go

@@ -236,9 +236,11 @@ func run(opts *options) error {
 		IgnoreNonJSONOutputLines: opts.ignoreNonJSONOutputLines,
 	}
 	exec, err := testjson.ScanTestOutput(cfg)
+	handler.Flush()
 	if err != nil {
 		return finishRun(opts, exec, err)
 	}
+
 	exitErr := goTestProc.cmd.Wait()
 	if signum := atomic.LoadInt32(&goTestProc.signal); signum != 0 {
 		return finishRun(opts, exec, exitError{num: signalExitCode + int(signum)})
@@ -260,6 +262,7 @@ func run(opts *options) error {
 
 	cfg = testjson.ScanConfig{Execution: exec, Handler: handler}
 	exitErr = rerunFailed(ctx, opts, cfg)
+	handler.Flush()
 	if err := writeRerunFailsReport(opts, exec); err != nil {
 		return err
 	}

cmd/main_test.go

@@ -5,6 +5,8 @@ import (
 	"encoding/json"
 	"os"
 	"os/exec"
+	"path/filepath"
+	"runtime"
 	"strings"
 	"testing"
 
@@ -13,6 +15,7 @@ import (
 	"gotest.tools/v3/assert/cmp"
 	"gotest.tools/v3/env"
 	"gotest.tools/v3/golden"
+	"gotest.tools/v3/skip"
 )
 
 func TestUsage_WithFlagsFromSetupFlags(t *testing.T) {
@@ -445,3 +448,41 @@ func TestRun_InputFromStdin(t *testing.T) {
 	assert.NilError(t, err)
 	assert.Assert(t, cmp.Contains(stdout.String(), "DONE 1"))
 }
+
+func TestRun_JsonFileIsSyncedBeforePostRunCommand(t *testing.T) {
+	skip.If(t, runtime.GOOS == "windows")
+
+	input := golden.Get(t, "../../testjson/testdata/input/go-test-json.out")
+
+	fn := func(args []string) *proc {
+		return &proc{
+			cmd:    fakeWaiter{},
+			stdout: bytes.NewReader(input),
+			stderr: bytes.NewReader(nil),
+		}
+	}
+	reset := patchStartGoTestFn(fn)
+	defer reset()
+
+	tmp := t.TempDir()
+	jsonFile := filepath.Join(tmp, "json.log")
+
+	out := new(bytes.Buffer)
+	opts := &options{
+		rawCommand:  true,
+		args:        []string{"./test.test"},
+		format:      "none",
+		stdout:      out,
+		stderr:      os.Stderr,
+		hideSummary: &hideSummaryValue{value: testjson.SummarizeNone},
+		jsonFile:    jsonFile,
+		postRunHookCmd: &commandValue{
+			command: []string{"cat", jsonFile},
+		},
+	}
+	err := run(opts)
+	assert.NilError(t, err)
+	expected := string(input)
+	_, actual, _ := strings.Cut(out.String(), "s\n") // remove the DONE line
+	assert.Equal(t, actual, expected)
+}

cmd/watch.go

@@ -88,6 +88,7 @@ func runSingle(opts *options, dir string) (*testjson.Execution, error) {
 		Stop:    cancel,
 	}
 	exec, err := testjson.ScanTestOutput(cfg)
+	handler.Flush()
 	if err != nil {
 		return exec, finishRun(opts, exec, err)
 	}

testjson/format.go

@@ -256,6 +256,8 @@ type FormatOptions struct {
 // NewEventFormatter returns a formatter for printing events.
 func NewEventFormatter(out io.Writer, format string, formatOpts FormatOptions) EventFormatter {
 	switch format {
+	case "none":
+		return eventFormatterFunc(func(TestEvent, *Execution) error { return nil })
 	case "debug":
 		return &formatAdapter{out, debugFormat}
 	case "standard-json":