diff --git a/tests/test_data_model.py b/tests/test_data_model.py
new file mode 100644
index 0000000..7ad56a4
--- /dev/null
+++ b/tests/test_data_model.py
@@ -0,0 +1,55 @@
+import pytest
+from Whatsapp_Chat_Exporter.data_model import TimeZone, Timing
+from datetime import timedelta
+
+
+class TestTimeZone:
+    def test_utcoffset(self):
+        tz = TimeZone(5.5)
+        assert tz.utcoffset(None) == timedelta(hours=5.5)
+
+    def test_dst(self):
+        tz = TimeZone(2)
+        assert tz.dst(None) == timedelta(0)
+
+
+class TestTiming:   
+    @pytest.mark.parametrize("offset, expected_hour", [
+        (8, "08:00"),      # Integer (e.g., Hong Kong Standard Time)
+        (-8, "16:00"),     # Negative Integer (e.g., PST)
+        (5.5, "05:30"),    # Positive Float (e.g., IST)
+        (-3.5, "20:30"),   # Negative Float (e.g., Newfoundland)
+    ])
+
+    def test_format_timestamp_various_offsets(self, offset, expected_hour):
+        """Verify that both int and float offsets calculate time correctly."""
+        t = Timing(offset)
+        result = t.format_timestamp(1672531200, "%H:%M")
+        assert result == expected_hour
+
+    @pytest.mark.parametrize("ts_input", [
+        1672531200,        # Unix timestamp as int
+        1672531200.0,      # Unix timestamp as float
+    ])
+
+    def test_timestamp_input_types(self, ts_input):
+        """Verify the method accepts both int and float timestamps."""
+        t = Timing(0)
+        result = t.format_timestamp(ts_input, "%Y")
+        assert result == "2023"
+
+    def test_timing_none_offset(self):
+        """Verify initialization with None doesn't crash and uses system time."""
+        t = Timing(None)
+        assert t.tz is None
+        # Should still return a valid string based on local machine time without crashing
+        result = t.format_timestamp(1672531200, "%Y")
+        assert result == "2023"
+
+    def test_millisecond_scaling(self):
+        """Verify that timestamps in milliseconds are correctly scaled down."""
+        t = Timing(0)
+        # Milliseconds as int
+        assert t.format_timestamp(1672531200000, "%Y") == "2023"
+        # Milliseconds as float
+        assert t.format_timestamp(1672531200000.0, "%Y") == "2023"