Add nullable string tests

#19

Author: n1nj4t4nuk1

tests/unit/nullable_string_test.py

@@ -0,0 +1,29 @@
+import unittest
+
+from pyvalueobjects.strings.nullable_string import NullableString
+
+
+class TestNullableStringValueObject(unittest.TestCase):
+    def test_value_return_input_value(self):
+        vo = NullableString('')
+        self.assertEqual('', vo.value())
+
+    def test_from_string_method_returns_string(self):
+        vo = NullableString.from_int(39)
+        self.assertEqual('39', vo.value())
+
+    def test_from_float_method_returns_int_format_string(self):
+        vo = NullableString.from_float(39.0)
+        self.assertEqual('39.0', vo.value())
+
+    def test_zero_value_return_input_value(self):
+        vo = NullableString.from_int(0)
+        self.assertEqual('0', vo.value())
+
+    def test_basic_string(self):
+        vo = NullableString('patata')
+        self.assertEqual('patata', vo.value())
+
+    def test_none_return_none(self):
+        vo = NullableString(None)
+        self.assertEqual(None, vo.value())