Index: Lib/test/test_file_jy.py
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- Lib/test/test_file_jy.py	(revision 8156:623eaa3d7834cf8ac04cf420ecb9f40a1f37707b)
+++ Lib/test/test_file_jy.py	(revision 8156+:623eaa3d7834+)
@@ -7,6 +7,7 @@
 from test import test_support
 from java.lang import System
 
+
 class FileTestCase(unittest.TestCase):
 
     def tearDown(self):
@@ -47,8 +48,8 @@
     def test_issue2081(self):
         with open(test_support.TESTFN, 'wb'):
             pass
-        os.chmod(test_support.TESTFN, 200)      # write-only
-        with open(test_support.TESTFN, 'w'):    # should succeed, raised IOError (permission denied) prior to fix
+        os.chmod(test_support.TESTFN, 200)  # write-only
+        with open(test_support.TESTFN, 'w'):  # should succeed, raised IOError (permission denied) prior to fix
             pass
 
     # http://bugs.jython.org/issue2358
@@ -64,6 +65,37 @@
         with open('/proc/{}/cmdline'.format(os.getpid())) as f:
             self.assertIn('jython', f.read())
 
+    def test_issue2363(self):
+        # http://bugs/jython.org/issue2363
+        # relative seek using read() and readline()
+        with open(test_support.TESTFN, 'wb') as f:
+            f.write(b'To seek or not to seek,\nThat is the question.\n')
+            f.close()
+        with open(test_support.TESTFN, 'rb') as f:
+            f.read()
+            self.assertEqual(f.tell(), 46)
+            f.seek(-10, 1)
+            self.assertEqual(f.tell(), 36)
+            f.seek(5, 1)
+            self.assertEqual(f.tell(), 41)
+            f.seek(20)  # seek from a point
+            self.assertEqual(f.tell(), 20)
+            f.read()
+            self.assertEqual(f.tell(), 46)
+            # readline()
+            f.seek(0)
+            f.readline()
+            self.assertEqual(f.tell(), 24)
+            f.seek(-10, 1)
+            # fails...
+            # Seek does not start at last
+            # tell() pos which is 24
+            # It starts at last byte (46)
+            self.assertEqual(f.tell(), 14)
+            f.seek(5, 1)
+            self.assertEqual(f.tell(), 19)
+            f.close()
+
 
 def test_main():
     test_support.run_unittest(FileTestCase)