Added safe_var function

tests/unit/test_safe_var.py

@@ -0,0 +1,44 @@
+import unittest
+import sys
+import os
+from jinja2 import Undefined
+
+# Ensure filter_plugins directory is on the path
+sys.path.insert(
+    0,
+    os.path.abspath(os.path.join(os.path.dirname(__file__), '../../filter_plugins'))
+)
+
+from safe_var import FilterModule
+
+class TestSafeVarFilter(unittest.TestCase):
+    def setUp(self):
+        # Retrieve the safe_var filter function
+        self.filter = FilterModule().filters()['safe_var']
+
+    def test_returns_non_empty_string(self):
+        self.assertEqual(self.filter('hello'), 'hello')
+
+    def test_returns_empty_string(self):
+        self.assertEqual(self.filter(''), '')
+
+    def test_returns_empty_for_none(self):
+        self.assertEqual(self.filter(None), '')
+
+    def test_returns_empty_for_jinja_undefined(self):
+        # Instantiate an Undefined without arguments
+        undef = Undefined()
+        self.assertEqual(self.filter(undef), '')
+
+    def test_returns_zero_for_zero(self):
+        # 0 is falsey but not None or Undefined, so safe_var returns it
+        self.assertEqual(self.filter(0), 0)
+
+    def test_returns_list_and_dict_unchanged(self):
+        data = {'key': 'value'}
+        self.assertEqual(self.filter(data), data)
+        lst = [1, 2, 3]
+        self.assertEqual(self.filter(lst), lst)
+
+if __name__ == '__main__':
+    unittest.main()