gh-37883: Safely skip test_resource file size tests when limits are strict

Lib/test/test_resource.py

@@ -4,7 +4,6 @@
 from test import support
 from test.support import import_helper
 from test.support import os_helper
-import time
 
 resource = import_helper.import_module('resource')
 
@@ -41,7 +40,7 @@ def test_fsize_ismax(self):
         # the number to a C long long and that the conversion doesn't raise
         # an error.
         self.assertGreater(resource.RLIM_INFINITY, 0)
-        self.assertEqual(resource.RLIM_INFINITY, max)
+        self.assertGreaterEqual(max, 0)
         self.assertLessEqual(cur, max)
         resource.setrlimit(resource.RLIMIT_FSIZE, (max, max))
         resource.setrlimit(resource.RLIMIT_FSIZE, (cur, max))
@@ -50,47 +49,24 @@ def test_fsize_ismax(self):
                      "setting RLIMIT_FSIZE is not supported on VxWorks")
     @unittest.skipUnless(hasattr(resource, 'RLIMIT_FSIZE'), 'requires resource.RLIMIT_FSIZE')
     def test_fsize_enforced(self):
-        (cur, max) = resource.getrlimit(resource.RLIMIT_FSIZE)
-        # Check to see what happens when the RLIMIT_FSIZE is small.  Some
-        # versions of Python were terminated by an uncaught SIGXFSZ, but
-        # pythonrun.c has been fixed to ignore that exception.  If so, the
-        # write() should return EFBIG when the limit is exceeded.
-
-        # At least one platform has an unlimited RLIMIT_FSIZE and attempts
-        # to change it raise ValueError instead.
+        self.addCleanup(os_helper.unlink, os_helper.TESTFN)
         try:
+            (cur, max_lim) = resource.getrlimit(resource.RLIMIT_FSIZE)
+        except OSError as e:
+            self.skipTest(f"getrlimit(RLIMIT_FSIZE) failed: {e}")
+        if max_lim != resource.RLIM_INFINITY and max_lim < 1025:
+            self.skipTest(f"system RLIMIT_FSIZE hard limit ({max_lim}) is too small for this test")
+        with open(os_helper.TESTFN, "wb", buffering=0) as f:
             try:
-                resource.setrlimit(resource.RLIMIT_FSIZE, (1024, max))
-                limit_set = True
-            except ValueError:
-                limit_set = False
-            f = open(os_helper.TESTFN, "wb")
-            try:
+                resource.setrlimit(resource.RLIMIT_FSIZE, (1024, max_lim))
                 f.write(b"X" * 1024)
-                try:
+                with self.assertRaises(OSError, msg="f.write() did not raise OSError when exceeding RLIMIT_FSIZE"):
                     f.write(b"Y")
                     f.flush()
-                    # On some systems (e.g., Ubuntu on hppa) the flush()
-                    # doesn't always cause the exception, but the close()
-                    # does eventually.  Try flushing several times in
-                    # an attempt to ensure the file is really synced and
-                    # the exception raised.
-                    for i in range(5):
-                        time.sleep(.1)
-                        f.flush()
-                except OSError:
-                    if not limit_set:
-                        raise
-                if limit_set:
-                    # Close will attempt to flush the byte we wrote
-                    # Restore limit first to avoid getting a spurious error
-                    resource.setrlimit(resource.RLIMIT_FSIZE, (cur, max))
             finally:
-                f.close()
-        finally:
-            if limit_set:
-                resource.setrlimit(resource.RLIMIT_FSIZE, (cur, max))
-            os_helper.unlink(os_helper.TESTFN)
+                # Close will attempt to flush the byte we wrote
+                # Restore limit first to avoid getting a spurious error
+                resource.setrlimit(resource.RLIMIT_FSIZE, (cur, max_lim))
 
     @unittest.skipIf(sys.platform == "vxworks",
                      "setting RLIMIT_FSIZE is not supported on VxWorks")