Add nullable CPE tests

Close #27

Author: n1nj4t4nuk1

tests/security/nullable_cpe_test.py

@@ -0,0 +1,18 @@
+import unittest
+
+from pyvalueobjects.errors.ValueObjectError import ValueObjectError
+from pyvalueobjects.security.nullable_cpe import NullableCpe
+
+
+class TestNullableCpeValueObject(unittest.TestCase):
+    def test_value_return_input_value(self):
+        self.assertRaises(ValueObjectError, NullableCpe, '')
+
+    def test_basic_cpe(self):
+        vo = NullableCpe('cpe:/a:openjdk:openjdk:8u282')
+        self.assertEqual('cpe:/a:openjdk:openjdk:8u282', vo.value())
+
+    def test_none_return_none(self):
+        vo = NullableCpe(None)
+        self.assertEqual(None, vo.value())
+