filebeat: fix misnamed OS-suffixed test files so they actually run (#51853) (#51917)

Four test files in filebeat/input/ embedded a GOOS token in the middle of
their name (`*_test_<goos>.go`) instead of ending in `_test.go`. Go only
treats files ending in `_test.go` as test files, and it derives an implicit
build constraint from a trailing `_<goos>` suffix. The combination meant
these files were never considered tests on any platform:

- filestream/{filestream,fswatch,identifier}_test_non_windows.go carried
  `//go:build !windows`, while the `_windows` suffix imposed an implicit
  `GOOS=windows` constraint. `windows && !windows` is never satisfiable, so
  they were dropped on every platform (they showed up in .IgnoredGoFiles).
- file/identifier_test_windows.go (`//go:build windows`) did compile on
  Windows, but as ordinary package source rather than a test file, so
  `go test` never registered its Test func -- and it linked `testing` into
  the production Windows binary of the file input.

As a result, 7 Test functions covering symlink handling, file
rename/remove/truncate detection and inode-marker identity had not run
since ~2020, hiding any regressions from CI. Because they never compiled,
they had also drifted out of sync with the code under test.

Changes:

- Rename to valid, correctly-constrained test files, keeping the build tags:
    filestream_test_non_windows.go  -> filestream_nonwindows_test.go
    identifier_test_non_windows.go  -> identifier_nonwindows_test.go
    file/identifier_test_windows.go -> identifier_windows_test.go
- Repair the reactivated filestream tests against current APIs
  (newFileReader/newFileScanner signatures, FSEvent.Descriptor instead of the
  removed FSEvent.Info, modern test helpers, t.TempDir).
- Delete fswatch_test_non_windows.go: its three tests
  (TestFileScannerSymlinks, TestFileWatcherRenamedFile,
  TestFileWatcherRenamedTruncated) duplicate coverage already provided by the
  live TestFileScanner, TestFileWatcher and
  TestFileWatcherCopyTruncateWithFingerprint, and depended on the removed
  fileWatcher.sameFileFunc injection point.

Net effect: TestLogFileRenamed, TestLogFileRemoved and
TestFileIdentifierInodeMarker now run on non-Windows, TestInodeMarkerError
now runs on Windows, and the file input's production Windows binary no longer
imports testing. fswatch_test_non_windows.go was deletes, other tests already
covered what it was supposed to cover.

Assisted-By: Claude Code
(cherry picked from commit 2a20583)

Co-authored-by: Anderson Queiroz <anderson.queiroz@elastic.co>

Author: mergify[bot]

…at/input/file/identifier_test_windows.go …at/input/file/identifier_windows_test.gofilebeat/input/file/identifier_test_windows.go renamed to filebeat/input/file/identifier_windows_test.go filebeat/input/file/identifier_test_windows.go renamed to filebeat/input/file/identifier_windows_test.go

@@ -22,24 +22,26 @@ package filestream
 import (
 	"context"
 	"os"
+	"path/filepath"
 	"testing"
 	"time"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 
 	"github.com/elastic/elastic-agent-libs/logp/logptest"
 )
 
 // these tests are separated as one cannot delete/rename files
 // while another process is working with it on Windows
 func TestLogFileRenamed(t *testing.T) {
-	f := createTestLogFile()
+	f := createTestLogFile(t)
 	defer f.Close()
 
 	renamedFile := f.Name() + ".renamed"
 
 	reader, _, err := newFileReader(
-		logptest.NewTestingLogger(t, ""),
+		logptest.NewFileLogger(t, filepath.Join("..", "..", "build", "integration-tests")).Logger,
 		context.TODO(),
 		f,
 		readerConfig{},
@@ -57,7 +59,7 @@ func TestLogFileRenamed(t *testing.T) {
 
 	buf := make([]byte, 1024)
 	_, err = reader.Read(buf)
-	assert.Nil(t, err)
+	assert.NoError(t, err)
 
 	err = os.Rename(f.Name(), renamedFile)
 	if err != nil {
@@ -71,11 +73,11 @@ func TestLogFileRenamed(t *testing.T) {
 }
 
 func TestLogFileRemoved(t *testing.T) {
-	f := createTestLogFile()
+	f := createTestLogFile(t)
 	defer f.Close()
 
 	reader, _, err := newFileReader(
-		logptest.NewTestingLogger(t, ""),
+		logptest.NewFileLogger(t, filepath.Join("..", "..", "build", "integration-tests")).Logger,
 		context.TODO(),
 		f,
 		readerConfig{},
@@ -93,7 +95,7 @@ func TestLogFileRemoved(t *testing.T) {
 
 	buf := make([]byte, 1024)
 	_, err = reader.Read(buf)
-	assert.Nil(t, err)
+	assert.NoError(t, err)
 
 	err = os.Remove(f.Name())
 	if err != nil {
@@ -104,3 +106,16 @@ func TestLogFileRemoved(t *testing.T) {
 
 	assert.Equal(t, ErrClosed, err)
 }
+
+// createTestLogFile creates a temporary plain-text log file with a few lines of
+// content, wrapped as a filestream File ready to be passed to newFileReader.
+func createTestLogFile(t *testing.T) File {
+	t.Helper()
+	fs := filestream{
+		readerConfig: readerConfig{BufferSize: 512},
+		compression:  CompressionNone,
+	}
+	f, err := fs.newFile(createTestPlainLogFile(t))
+	require.NoError(t, err, "could not create test log file")
+	return f
+}

…ilestream/filestream_test_non_windows.go …filestream/filestream_nonwindows_test.gofilebeat/input/filestream/filestream_test_non_windows.go renamed to filebeat/input/filestream/filestream_nonwindows_test.go filebeat/input/filestream/filestream_test_non_windows.go renamed to filebeat/input/filestream/filestream_nonwindows_test.go

@@ -20,8 +20,8 @@
 package filestream
 
 import (
-	"io/ioutil"
 	"os"
+	"path/filepath"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -30,22 +30,23 @@ import (
 	loginp "github.com/elastic/beats/v7/filebeat/input/filestream/internal/input-logfile"
 	"github.com/elastic/beats/v7/libbeat/common/file"
 	conf "github.com/elastic/elastic-agent-libs/config"
+	"github.com/elastic/elastic-agent-libs/logp/logptest"
 )
 
 func TestFileIdentifierInodeMarker(t *testing.T) {
 	t.Run("inode_marker file identifier", func(t *testing.T) {
 		const markerContents = "unique_marker"
-		markerFile, err := ioutil.TempFile("", "test_file_identifier_inode_marker_identifier")
+		dir := t.TempDir()
+		markerFile, err := os.Create(filepath.Join(dir, "marker"))
 		if err != nil {
 			t.Fatalf("cannot create marker file for test: %v", err)
 		}
-		defer os.Remove(markerFile.Name())
 
 		_, err = markerFile.Write([]byte(markerContents))
 		if err != nil {
 			t.Fatalf("cannot write marker contents to file: %v", err)
 		}
-		markerFile.Sync()
+		require.NoError(t, markerFile.Sync())
 
 		c := conf.MustNewConfigFrom(map[string]interface{}{
 			"identifier": map[string]interface{}{
@@ -58,24 +59,23 @@ func TestFileIdentifierInodeMarker(t *testing.T) {
 		err = c.Unpack(&cfg)
 		require.NoError(t, err)
 
-		identifier, err := newFileIdentifier(cfg.Identifier)
+		identifier, err := newFileIdentifier(cfg.Identifier, "", logptest.NewTestingLogger(t, ""))
 		require.NoError(t, err)
 		assert.Equal(t, inodeMarkerName, identifier.Name())
 
-		tmpFile, err := ioutil.TempFile("", "test_file_identifier_inode_marker")
+		tmpFile, err := os.Create(filepath.Join(dir, "target"))
 		if err != nil {
 			t.Fatalf("cannot create temporary file for test: %v", err)
 		}
-		defer os.Remove(tmpFile.Name())
 
 		fi, err := tmpFile.Stat()
 		if err != nil {
 			t.Fatalf("cannot stat temporary file for test: %v", err)
 		}
 
 		fsEvent := loginp.FSEvent{
-			NewPath: tmpFile.Name(),
-			Info:    fi,
+			NewPath:    tmpFile.Name(),
+			Descriptor: loginp.FileDescriptor{Info: file.ExtendFileInfo(fi)},
 		}
 		src := identifier.GetSource(fsEvent)
 
@@ -87,7 +87,7 @@ func TestFileIdentifierInodeMarker(t *testing.T) {
 		if err != nil {
 			t.Fatalf("cannot write marker contents to file: %v", err)
 		}
-		markerFile.Sync()
+		require.NoError(t, markerFile.Sync())
 
 		src = identifier.GetSource(fsEvent)