[chore][pkg/stanza] Add tests for reader.Validate (#30623)

Depends on #30449

pkg/stanza/fileconsumer/internal/reader/validate_test.go

@@ -0,0 +1,142 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package reader
+
+import (
+	"context"
+	"os"
+	"runtime"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/stanza/fileconsumer/internal/filetest"
+)
+
+// When a file it moved, we should detect that our old handle is still valid.
+func TestValidateMoved(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("Moving files while open is unsupported on Windows")
+	}
+	t.Parallel()
+
+	tempDir := t.TempDir()
+	temp := filetest.OpenTemp(t, tempDir)
+	_, err := temp.WriteString("testlog1\n")
+	require.NoError(t, err)
+
+	f, sink := testFactory(t)
+	fp, err := f.NewFingerprint(temp)
+	require.NoError(t, err)
+
+	reader, err := f.NewReader(temp, fp)
+	require.NoError(t, err)
+
+	reader.ReadToEnd(context.Background())
+	sink.ExpectToken(t, []byte("testlog1"))
+
+	// Validate before moving
+	assert.True(t, reader.Validate())
+
+	// Move the file
+	require.NoError(t, os.Rename(temp.Name(), temp.Name()+".old"))
+
+	// Validate after moving
+	assert.True(t, reader.Validate())
+
+	_, err = temp.WriteString("testlog2\n")
+	require.NoError(t, err)
+
+	reader.ReadToEnd(context.Background())
+	sink.ExpectToken(t, []byte("testlog2"))
+
+	// Validate after writing to the moved file
+	assert.True(t, reader.Validate())
+}
+
+func TestInvalidateTruncated(t *testing.T) {
+	t.Parallel()
+
+	tempDir := t.TempDir()
+	temp := filetest.OpenTemp(t, tempDir)
+	_, err := temp.WriteString("testlog1\n")
+	require.NoError(t, err)
+
+	f, sink := testFactory(t)
+	fp, err := f.NewFingerprint(temp)
+	require.NoError(t, err)
+
+	reader, err := f.NewReader(temp, fp)
+	require.NoError(t, err)
+
+	reader.ReadToEnd(context.Background())
+	sink.ExpectToken(t, []byte("testlog1"))
+
+	// Validate before truncating
+	assert.True(t, reader.Validate())
+
+	// Truncate the file
+	require.NoError(t, temp.Truncate(0))
+
+	// Invalidate after truncating
+	assert.False(t, reader.Validate())
+
+	// Write different content to the file
+	_, err = temp.WriteString("testlog2\n")
+	require.NoError(t, err)
+
+	// Still invalid
+	assert.False(t, reader.Validate())
+}
+
+func TestInvalidateClosed(t *testing.T) {
+	t.Parallel()
+
+	tempDir := t.TempDir()
+	temp := filetest.OpenTemp(t, tempDir)
+	_, err := temp.WriteString("testlog1\n")
+	require.NoError(t, err)
+
+	f, _ := testFactory(t)
+	fp, err := f.NewFingerprint(temp)
+	require.NoError(t, err)
+
+	reader, err := f.NewReader(temp, fp)
+	require.NoError(t, err)
+
+	// Validate before closing
+	assert.True(t, reader.Validate())
+
+	// Close the file using the reader to drop the handle.
+	reader.Close()
+
+	// Invalidate after closing
+	assert.False(t, reader.Validate())
+}
+
+func TestInvalidateUnreadable(t *testing.T) {
+	t.Parallel()
+
+	tempDir := t.TempDir()
+	temp := filetest.OpenTemp(t, tempDir)
+	_, err := temp.WriteString("testlog1\n")
+	require.NoError(t, err)
+
+	f, _ := testFactory(t)
+	fp, err := f.NewFingerprint(temp)
+	require.NoError(t, err)
+
+	reader, err := f.NewReader(temp, fp)
+	require.NoError(t, err)
+
+	// Validate before closing
+	assert.True(t, reader.Validate())
+
+	// Close the file using our direct handle. The reader still has a handle but cannot be read.
+	require.NoError(t, temp.Close())
+
+	// Invalidate unreadable file
+	assert.False(t, reader.Validate())
+}