test: fix tests according curie specification

According the CURIE syntax specification [1] "The prefix is separated
from the reference by a colon (:). It is possible to omit both the
prefix and the colon [...]." But a test case existed expecting a CURIE
omitting both prefix and colon to be invalid.

This patch fixes this wrong expectation.

[1]: https://www.w3.org/TR/curie/#s_syntax

Signed-off-by: Silvano Cirujano Cuesta <silvano.cirujano-cuesta@siemens.com>

Author: Silvanoc

tests/test_utils/test_metamodelcore.py

@@ -59,9 +59,7 @@ def test_uriorcuries(self):
     def test_curie(self):
         """ Test the CURIE type """
         self.assertEqual("rdf:type", Curie("rdf:type"))
-        with self.assertRaises(ValueError):
-            Curie("type")
-        self.assertFalse(Curie.is_valid("type"))
+        self.assertTrue(Curie.is_valid("type"))
         self.assertEqual(":type", Curie(":type"))
         self.assertTrue(Curie.is_valid(':type'))
         self.assertTrue(Curie.is_valid('WIKIDATA_PROPERTY:P854'))