use filepath for correct path in unittest

internal/core/processing_test.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"net/http"
 	"net/http/httptest"
+	"path/filepath"
 	"testing"
 
 	"github.com/go-shiori/shiori/internal/core"
@@ -45,6 +46,7 @@ func TestDownloadBookImage(t *testing.T) {
 			assert.True(t, deps.Domains.Storage.FileExists(dstFile))
 		})
 		t.Run("successful download medium size image", func(t *testing.T) {
+			tempDir := t.TempDir()
 			// create a file server handler for the 'testdata' directory
 			fs := http.FileServer(http.Dir("../../testdata/"))
 
@@ -54,7 +56,7 @@ func TestDownloadBookImage(t *testing.T) {
 
 			// Arrange
 			imageURL := server.URL + "/medium_image.png"
-			dstFile := "tempDir/medium_image.png"
+			dstFile := filepath.Join(tempDir, "medium_image.png")
 
 			// Act
 			err := core.DownloadBookImage(deps, imageURL, dstFile)