avocado.core.test: Check for basename length, not full path

only the basename of the `self.filename` has to be shorter than
maxsize-5, not the full path.

Also the IOError in selftest is rather misleading as it relates to
missing source file. Let's just check the path is correctly set and
additionally verify `_record_reference_*` is not crashing when filename
not associated.
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>

avocado/core/test.py

@@ -174,7 +174,8 @@ class Test(unittest.TestCase):
         Returns the path to the directory that contains test data files
         """
         # Maximal allowed file name length is 255
-        if self.filename is not None and len(self.filename) < 251:
+        if (self.filename is not None and
+                len(os.path.basename(self.filename)) < 251):
             return self.filename + '.data'
         else:
             return None

selftests/unit/test_test.py

@@ -67,12 +67,14 @@ class TestClassTestUnit(unittest.TestCase):
         self.assertEqual(os.path.basename(test.workdir),
                          os.path.basename(test.logdir))
         flexmock(test)
-        test.should_receive('filename').and_return("a"*250)
-        self.assertEqual("a"*250 + ".data", test.datadir)
-        self.assertRaises(IOError, test._record_reference_stdout)
-        self.assertRaises(IOError, test._record_reference_stderr)
+        test.should_receive('filename').and_return(os.path.join(self.tmpdir,
+                                                                "a"*250))
+        self.assertEqual(os.path.join(self.tmpdir, "a"*250 + ".data"),
+                         test.datadir)
         test.should_receive('filename').and_return("a"*251)
         self.assertFalse(test.datadir)
+        test._record_reference_stdout       # Should does nothing
+        test._record_reference_stderr       # Should does nothing
         test._record_reference_stdout()
         test._record_reference_stderr()