Fixed and optimized a test of issue #22526.

Lib/test/test_file2k.py

@@ -14,7 +14,7 @@ except ImportError:
     threading = None
 
 from test import test_support
-from test.test_support import TESTFN, run_unittest
+from test.test_support import TESTFN, run_unittest, requires
 from UserList import UserList
 
 class AutoFileTests(unittest.TestCase):
@@ -437,16 +437,18 @@ class OtherFileTests(unittest.TestCase):
             f.close()
 
     @unittest.skipUnless(sys.maxsize > 2**31, "requires 64-bit system")
-    @test_support.precisionbigmemtest(2**31, 1)
-    def test_very_long_line(self, maxsize):
+    @test_support.precisionbigmemtest(2**31, 2.5, dry_run=False)
+    def test_very_long_line(self, size):
         # Issue #22526
+        requires('largefile')
         with open(TESTFN, "wb") as fp:
-            fp.write("\0"*2**31)
+            fp.seek(size - 1)
+            fp.write("\0")
         with open(TESTFN, "rb") as fp:
             for l in fp:
                 pass
-        self.assertEqual(len(l), 2**31)
-        self.assertEqual(l.count("\0"), 2**31)
+        self.assertEqual(len(l), size)
+        self.assertEqual(l.count("\0"), size)
         l = None
 
 class FileSubclassTests(unittest.TestCase):