Fixed tell position after seek in append mode

- fixes #363

CHANGES.md

@@ -13,6 +13,14 @@ The release versions are PyPi releases.
   * use README.md in pypi ([#358](../../issues/358))
 
 #### Fixes
+  * `tell` after `seek` gave incorrect result in append mode 
+  ([#363](../../issues/363))
+  * a failing pytest did not display the test function correctly 
+  ([#381](../../issues/381))
+  * flushing file contents after truncate was incorrect under some conditions 
+  ([#412](../../issues/412))
+  * `readline()` did not work correctly in binary mode 
+  ([#411](../../issues/411))
   *  `pathlib.Path.resolve()` behaved incorrectly if the path does not exist
   ([#401](../../issues/401))
   * `closed` attribute was not implemented in fake file ([#380](../../issues/380))

pyfakefs/fake_filesystem.py

@@ -4420,7 +4420,7 @@ def tell(self):
         self._check_open_file()
         if self._flushes_after_tell():
             self.flush()
-            if self._read_seek:
+            if 0 < self._read_seek < self._flush_pos:
                 self._read_seek = self._flush_pos
                 self._read_whence = 0
 

pyfakefs/tests/fake_os_test.py

@@ -1210,6 +1210,13 @@ def test_append_mode_tell_macos(self):
         self.check_macos_only()
         self.check_append_mode_tell_after_truncate(7)
 
+    def test_tell_after_seek_in_append_mode(self):
+        # Regression test for #363
+        file_path = self.make_path('foo')
+        with self.open(file_path, 'a') as f:
+            f.seek(1)
+            self.assertEqual(1, f.tell())
+
     def test_dir_with_trailing_sep_is_dir(self):
         # regression test for #387
         self.assertTrue(self, self.os.path.isdir(self.base_path + self.os.sep))