Add non empty string tests

#2

Author: n1nj4t4nuk1

tests/strings/non_empty_string_test.py

@@ -0,0 +1,16 @@
+import unittest
+
+from pyvalueobjects.errors.ValueObjectError import ValueObjectError
+from pyvalueobjects.strings.non_empty_string import NonEmptyString
+
+
+class TestNonemptyStringValueObject(unittest.TestCase):
+    def test_value_return_input_value(self):
+        self.assertRaises(ValueObjectError, NonEmptyString, '')
+
+    def test_basic_string(self):
+        vo = NonEmptyString('patata')
+        self.assertEqual('patata', vo.value())
+
+    def test_none_return_none(self):
+        self.assertRaises(ValueObjectError, NonEmptyString, None)