fix: PersistentFile.toString() doesn't throw (#796)

* fix: PersistentFile.toString() doesn't throw

* add test

Author: pedroslopez

src/PersistentFile.js

@@ -45,7 +45,7 @@ class PersistentFile extends EventEmitter {
   }
 
   toString() {
-    return `PersistentFile: ${this._file.newFilename}, Original: ${this._file.originalFilename}, Path: ${this._file.filepath}`;
+    return `PersistentFile: ${this.newFilename}, Original: ${this.originalFilename}, Path: ${this.filepath}`;
   }
 
   write(buffer, cb) {

test/unit/persistent-file.test.js

@@ -9,6 +9,7 @@ const file = new PersistentFile({
   type: 'image/png',
   lastModifiedDate: now,
   originalFilename: 'cat.png',
+  newFilename: 'dff1d2eaab9752165764dcd00',
   mimetype: 'image/png',
 });
 
@@ -31,6 +32,11 @@ describe('PersistentFile', () => {
     expect(obj.originalFilename).toBe('cat.png');
   });
 
+  test('toString()', () => {
+    const result = file.toString();
+    expect(result).toBe('PersistentFile: dff1d2eaab9752165764dcd00, Original: cat.png, Path: /tmp/cat.png')
+  });
+
   test('destroy()', () => {
     file.open();
     file.destroy();