diff -r 0b2d4089180c Lib/test/test_tarfile.py
--- a/Lib/test/test_tarfile.py	Wed Apr 10 17:01:38 2013 -0400
+++ b/Lib/test/test_tarfile.py	Thu Apr 11 13:52:24 2013 -0500
@@ -26,6 +26,15 @@
 except ImportError:
     lzma = None
 
+def skipUnlessCompressionModule(name):
+    """
+    Skip if the specified compression module is not available.  Must be a
+    string, currently any of 'gzip', 'bz2', or 'lzma'.
+    """
+    if not globals()[name]:
+        return unittest.skip('{} not available'.format(name))
+    return lambda x:x
+
 def md5sum(data):
     return md5(data).hexdigest()
 
@@ -173,7 +182,7 @@
         self._test_fileobj_link("symtype2", "ustar/regtype")
 
 
-class CommonReadTest(ReadTest):
+class CommonReadTest:
 
     def test_empty_tarfile(self):
         # Test for issue6123: Allow opening empty archives.
@@ -227,7 +236,7 @@
                 tar.close()
 
 
-class MiscReadTest(CommonReadTest):
+class MiscReadTest(CommonReadTest, ReadTest):
 
     def test_no_name_argument(self):
         if self.mode.endswith(("bz2", "xz")):
@@ -416,7 +425,7 @@
             support.unlink(empty)
 
 
-class StreamReadTest(CommonReadTest):
+class StreamReadTest(CommonReadTest, ReadTest):
 
     mode="r|"
 
@@ -652,7 +661,7 @@
         self._test_member(tarinfo, size=7011, chksum=md5_regtype)
 
 
-class LongnameTest(ReadTest):
+class LongnameTest:
 
     def test_read_longname(self):
         # Test reading of longname (bug #1471427).
@@ -691,7 +700,7 @@
             self.assertEqual(tarinfo.type, self.longnametype)
 
 
-class GNUReadTest(LongnameTest):
+class GNUReadTest(ReadTest, LongnameTest):
 
     subdir = "gnu"
     longnametype = tarfile.GNUTYPE_LONGNAME
@@ -745,7 +754,7 @@
             return False
 
 
-class PaxReadTest(LongnameTest):
+class PaxReadTest(ReadTest, LongnameTest):
 
     subdir = "pax"
     longnametype = tarfile.XHDTYPE
@@ -786,7 +795,7 @@
             tar.close()
 
 
-class WriteTestBase(unittest.TestCase):
+class WriteTestBase:
     # Put all write tests in here that are supposed to be tested
     # in all possible mode combinations.
 
@@ -798,7 +807,7 @@
         self.assertTrue(fobj.closed is False, "external fileobjs must never closed")
 
 
-class WriteTest(WriteTestBase):
+class WriteTest(WriteTestBase, unittest.TestCase):
 
     mode = "w:"
 
@@ -1086,7 +1095,7 @@
             os.chdir(cwd)
 
 
-class StreamWriteTest(WriteTestBase):
+class StreamWriteTest(WriteTestBase, unittest.TestCase):
 
     mode = "w|"
 
@@ -1218,6 +1227,7 @@
                    ("longlnk/" * 127) + "longlink_")
 
 
+@unittest.skipUnless(hasattr(os, 'link'), 'os.link not available')
 class HardlinkTest(unittest.TestCase):
     # Test the creation of LNKTYPE (hardlink) members in an archive.
 
@@ -1702,6 +1712,8 @@
             self.assertTrue(tar.closed, "context manager failed")
 
 
+@unittest.skipIf(hasattr(os, 'link'),
+                 'link emulation is disabled when os.link is available')
 class LinkEmulationTest(ReadTest):
 
     # Test for issue #8741 regression. On platforms that do not support
@@ -1735,7 +1747,7 @@
     def test_symlink_extraction2(self):
         self._test_link_extraction("./ustar/linktest2/symtype")
 
-
+@skipUnlessCompressionModule('gzip')
 class GzipMiscReadTest(MiscReadTest):
     tarname = gzipname
     mode = "r:gz"
@@ -1747,32 +1759,42 @@
             tarfile.open("xxx", self.mode)
         self.assertEqual(ex.exception.errno, errno.ENOENT)
 
+@skipUnlessCompressionModule('gzip')
 class GzipUstarReadTest(UstarReadTest):
     tarname = gzipname
     mode = "r:gz"
+@skipUnlessCompressionModule('gzip')
 class GzipStreamReadTest(StreamReadTest):
     tarname = gzipname
     mode = "r|gz"
+@skipUnlessCompressionModule('gzip')
 class GzipWriteTest(WriteTest):
     mode = "w:gz"
+@skipUnlessCompressionModule('gzip')
 class GzipStreamWriteTest(StreamWriteTest):
     mode = "w|gz"
 
 
+@skipUnlessCompressionModule('bz2')
 class Bz2MiscReadTest(MiscReadTest):
     tarname = bz2name
     mode = "r:bz2"
+@skipUnlessCompressionModule('bz2')
 class Bz2UstarReadTest(UstarReadTest):
     tarname = bz2name
     mode = "r:bz2"
+@skipUnlessCompressionModule('bz2')
 class Bz2StreamReadTest(StreamReadTest):
     tarname = bz2name
     mode = "r|bz2"
+@skipUnlessCompressionModule('bz2')
 class Bz2WriteTest(WriteTest):
     mode = "w:bz2"
+@skipUnlessCompressionModule('bz2')
 class Bz2StreamWriteTest(StreamWriteTest):
     mode = "w|bz2"
 
+@skipUnlessCompressionModule('bz2')
 class Bz2PartialReadTest(unittest.TestCase):
     # Issue5068: The _BZ2Proxy.read() method loops forever
     # on an empty or partial bzipped file.
@@ -1803,102 +1825,58 @@
         self._test_partial_input("r:bz2")
 
 
+@skipUnlessCompressionModule('lzma')
 class LzmaMiscReadTest(MiscReadTest):
     tarname = xzname
     mode = "r:xz"
+@skipUnlessCompressionModule('lzma')
 class LzmaUstarReadTest(UstarReadTest):
     tarname = xzname
     mode = "r:xz"
+@skipUnlessCompressionModule('lzma')
 class LzmaStreamReadTest(StreamReadTest):
     tarname = xzname
     mode = "r|xz"
+@skipUnlessCompressionModule('lzma')
 class LzmaWriteTest(WriteTest):
     mode = "w:xz"
+@skipUnlessCompressionModule('lzma')
 class LzmaStreamWriteTest(StreamWriteTest):
     mode = "w|xz"
 
 
-def test_main():
+def setUpModule():
     support.unlink(TEMPDIR)
     os.makedirs(TEMPDIR)
 
-    tests = [
-        UstarReadTest,
-        MiscReadTest,
-        StreamReadTest,
-        DetectReadTest,
-        MemberReadTest,
-        GNUReadTest,
-        PaxReadTest,
-        WriteTest,
-        StreamWriteTest,
-        GNUWriteTest,
-        PaxWriteTest,
-        UstarUnicodeTest,
-        GNUUnicodeTest,
-        PAXUnicodeTest,
-        AppendTest,
-        LimitsTest,
-        MiscTest,
-        ContextManagerTest,
-    ]
-
-    if hasattr(os, "link"):
-        tests.append(HardlinkTest)
+    if any((gzip, bz2, lzma)):
+        with open(tarname, "rb") as fobj:
+            data = fobj.read()
     else:
-        tests.append(LinkEmulationTest)
-
-    with open(tarname, "rb") as fobj:
-        data = fobj.read()
+        return
 
     if gzip:
-        # Create testtar.tar.gz and add gzip-specific tests.
+        # Create testtar.tar.gz
         support.unlink(gzipname)
         with gzip.open(gzipname, "wb") as tar:
             tar.write(data)
 
-        tests += [
-            GzipMiscReadTest,
-            GzipUstarReadTest,
-            GzipStreamReadTest,
-            GzipWriteTest,
-            GzipStreamWriteTest,
-        ]
-
     if bz2:
-        # Create testtar.tar.bz2 and add bz2-specific tests.
+        # Create testtar.tar.bz2
         support.unlink(bz2name)
         with bz2.BZ2File(bz2name, "wb") as tar:
             tar.write(data)
 
-        tests += [
-            Bz2MiscReadTest,
-            Bz2UstarReadTest,
-            Bz2StreamReadTest,
-            Bz2WriteTest,
-            Bz2StreamWriteTest,
-            Bz2PartialReadTest,
-        ]
-
     if lzma:
-        # Create testtar.tar.xz and add lzma-specific tests.
+        # Create testtar.tar.xz
         support.unlink(xzname)
         with lzma.LZMAFile(xzname, "w") as tar:
             tar.write(data)
 
-        tests += [
-            LzmaMiscReadTest,
-            LzmaUstarReadTest,
-            LzmaStreamReadTest,
-            LzmaWriteTest,
-            LzmaStreamWriteTest,
-        ]
 
-    try:
-        support.run_unittest(*tests)
-    finally:
-        if os.path.exists(TEMPDIR):
-            shutil.rmtree(TEMPDIR)
+def tearDownModule():
+    if os.path.exists(TEMPDIR):
+        shutil.rmtree(TEMPDIR)
 
 if __name__ == "__main__":
-    test_main()
+    unittest.main()