diff --git a/internal/app_test.go b/internal/app_test.go
index 184951c..7c75b0c 100644
--- a/internal/app_test.go
+++ b/internal/app_test.go
@@ -52,6 +52,16 @@ func TestSanitizePresetName(t *testing.T) {
 			input:    "",
 			expected: "",
 		},
+		{
+			name:     "all_uppercase_letters",
+			input:    "ABCDEFG",
+			expected: "_______",
+		},
+		{
+			name:     "mixed_case_with_valid_chars",
+			input:    "aBcDeFg_123",
+			expected: "a_c_e_g____",
+		},
 	}
 
 	for _, tt := range tests {
diff --git a/internal/audioutils_test.go b/internal/audioutils_test.go
index ad61b3a..a004810 100644
--- a/internal/audioutils_test.go
+++ b/internal/audioutils_test.go
@@ -46,3 +46,21 @@ func TestWriteAudioFileSlices(t *testing.T) {
 		assert.Greater(t, (*audioFiles)[i].Duration, 0.0, "Duration should be positive")
 	}
 }
+
+// TestWriteAudioFileSlicesWithNonExistentFile verifies that the function correctly handles
+// errors when the input file doesn't exist.
+func TestWriteAudioFileSlicesWithNonExistentFile(t *testing.T) {
+	outputDir, err := os.MkdirTemp("", "test-output")
+	require.NoError(t, err, "Failed to create output directory")
+	defer os.RemoveAll(outputDir)
+
+	// Use a non-existent file path
+	nonExistentFilePath := "/path/to/nonexistent/file.wav"
+
+	audioFiles, err := writeAudioFileSlices(nonExistentFilePath, outputDir, 4, "test_prefix")
+
+	// Verify that the function returns an error
+	assert.Error(t, err, "writeAudioFileSlices should fail with non-existent file")
+	assert.Nil(t, audioFiles, "audioFiles should be nil when an error occurs")
+	assert.Contains(t, err.Error(), "could not open source file", "Error message should indicate the file couldn't be opened")
+}
diff --git a/internal/fileutils_test.go b/internal/fileutils_test.go
index b80e72d..5c23912 100644
--- a/internal/fileutils_test.go
+++ b/internal/fileutils_test.go
@@ -1,9 +1,12 @@
 package internal
 
 import (
+	"archive/zip"
 	ablmodels2 "github.com/alexfedosov/move-tool/internal/ablmodels"
+	"io"
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -78,6 +81,27 @@ func TestWritePresetFile(t *testing.T) {
 	assert.Greater(t, len(content), 0, "Preset file should not be empty")
 }
 
+// TestWritePresetFileWithInvalidDirectory verifies that the function correctly handles
+// errors when the output directory doesn't exist.
+func TestWritePresetFileWithInvalidDirectory(t *testing.T) {
+	// Use a non-existent directory
+	nonExistentDir := "/path/to/nonexistent/directory"
+
+	filePath := "TestPath"
+	audioFile := []ablmodels2.AudioFile{
+		{
+			FilePath: &filePath,
+			Duration: 1000.0,
+		},
+	}
+	preset := ablmodels2.NewDrumRackDevicePresetWithSamples(audioFile)
+
+	err := writePresetFile(preset, nonExistentDir)
+
+	// Verify that the function returns an error
+	assert.Error(t, err, "writePresetFile should fail with non-existent directory")
+}
+
 // TestArchivePresetBundle verifies that directories are correctly zipped into preset bundles
 // with the expected file structure and naming convention.
 func TestArchivePresetBundle(t *testing.T) {
@@ -112,4 +136,59 @@ func TestArchivePresetBundle(t *testing.T) {
 	zipPath := filepath.Join(outputDir, presetName+".ablpresetbundle")
 	_, err = os.Stat(zipPath)
 	assert.False(t, os.IsNotExist(err), "Archive file should exist at %s", zipPath)
+
+	// Verify the contents of the archive
+	extractDir, err := os.MkdirTemp("", "test-extract")
+	require.NoError(t, err, "Failed to create extraction directory")
+	defer os.RemoveAll(extractDir)
+
+	// Open the zip file
+	reader, err := zip.OpenReader(zipPath)
+	require.NoError(t, err, "Failed to open zip file")
+	defer reader.Close()
+
+	// Check that all expected files are in the archive
+	var foundFiles []string
+	for _, file := range reader.File {
+		foundFiles = append(foundFiles, file.Name)
+
+		// Extract and verify content of each file
+		rc, err := file.Open()
+		require.NoError(t, err, "Failed to open file in archive")
+
+		content, err := io.ReadAll(rc)
+		require.NoError(t, err, "Failed to read file content")
+		rc.Close()
+
+		// Verify content for non-directory entries
+		if !strings.HasSuffix(file.Name, "/") {
+			assert.Equal(t, testContent, content, "File content should match for %s", file.Name)
+		}
+	}
+
+	// Verify all expected files are in the archive
+	for _, expectedFile := range testFiles {
+		assert.Contains(t, foundFiles, expectedFile, "Archive should contain %s", expectedFile)
+	}
+}
+
+// TestArchivePresetBundleWithInvalidOutputDir verifies that the function correctly handles
+// errors when the output directory doesn't exist.
+func TestArchivePresetBundleWithInvalidOutputDir(t *testing.T) {
+	sourceDir, err := os.MkdirTemp("", "test-source")
+	require.NoError(t, err, "Failed to create source directory")
+	defer os.RemoveAll(sourceDir)
+
+	// Create a test file in the source directory
+	testFilePath := filepath.Join(sourceDir, "test.txt")
+	err = os.WriteFile(testFilePath, []byte("test content"), 0644)
+	require.NoError(t, err, "Failed to create test file")
+
+	// Use a non-existent output directory
+	nonExistentDir := "/path/to/nonexistent/directory"
+
+	err = archivePresetBundle("test_preset", sourceDir, nonExistentDir)
+
+	// Verify that the function returns an error
+	assert.Error(t, err, "archivePresetBundle should fail with non-existent output directory")
 }