diff --git a/tests/test_nmea/test_zda.py b/tests/test_nmea/test_zda.py
new file mode 100644
index 0000000..f255ef7
--- /dev/null
+++ b/tests/test_nmea/test_zda.py
@@ -0,0 +1,107 @@
+import calendar
+
+import pytest
+
+from nmea.zda import ggaDecode, zdaDecode, zdaDict2TIMESTAMP, zdaEpochSeconds
+
+
+def test_zda_decode_valid():
+    # Example from docstring
+    sentence = "$ZQZDA,110003.00,27,03,2006,-5,00*47"
+    result = zdaDecode(sentence)
+    expected = {
+        "timekeeper": "ZQ",
+        "localzonehour": -5,
+        "localzonemin": 0,
+        "hour": 11,
+        "min": 0,
+        "hsec": 0,
+        "sec": 3,
+        "mon": 3,
+        "year": 2006,
+        "day": 27,
+        "decimalsec": 3.0,
+    }
+    assert result == expected
+
+
+def test_zda_decode_invalid_length():
+    with pytest.raises(AssertionError):
+        zdaDecode("$ZQZDA,110")
+
+
+def test_zda_decode_invalid_start():
+    with pytest.raises(AssertionError):
+        zdaDecode("?ZQZDA,110003.00,27,03,2006,-5,00*47")
+
+
+def test_zda_decode_invalid_type():
+    with pytest.raises(AssertionError):
+        zdaDecode("$ZQRMC,110003.00,27,03,2006,-5,00*47")
+
+
+def test_zda_epoch_seconds():
+    sentence = "$ZQZDA,110003.00,27,03,2006,-5,00*47"
+    result = zdaEpochSeconds(sentence)
+    # Expected: calendar.timegm((2006, 3, 27, 11, 0, 3.0)) -> 1143457203
+    expected = calendar.timegm((2006, 3, 27, 11, 0, 3.0))
+    assert result == expected
+
+
+def test_gga_decode_valid():
+    # Example from docstring
+    sentence = "$GPGGA,152009.00,3652.48059177,N,07620.02018248,W,1,11,0.8,3.669,M,-34.579,M,,*57"
+    result = ggaDecode(sentence)
+    assert result["hour"] == "15"
+    assert result["min"] == "20"
+    assert result["sec"] == "09"
+    assert result["hsec"] == "00"
+    assert result["lat"] > 36.0
+    assert result["lon"] < -76.0
+    assert result["qual"] == 1
+    assert result["sats"] == 11
+    assert result["horz_dilution"] == 0.8
+    assert result["alt"] == 3.669
+    assert result["alt_units"] == "M"
+    assert result["geoidal_sep"] == -34.579
+    assert result["geoidal_sep_units"] == "M"
+    assert result["age"] is None
+
+
+def test_gga_decode_south_east():
+    # Custom sentence to test S/E lat/lon and age
+    sentence = "$GPGGA,152009.00,3652.48059177,S,07620.02018248,E,1,11,0.8,3.669,M,-34.579,M,1.5,*57"
+    result = ggaDecode(sentence)
+    assert result["lat"] < -36.0
+    assert result["lon"] > 76.0
+    assert result["age"] == 1.5
+
+
+def test_gga_decode_validate_true():
+    # Validate=True requires len >= 71 and <= 78
+    sentence = (
+        "$GPGGA,152009.00,3652.4800,N,07620.0200,W,1,11,0.8,3.669,M,-34.50,M,,*57"
+    )
+    assert 71 <= len(sentence) <= 78
+    result = ggaDecode(sentence, validate=True)
+    assert result["qual"] == 1
+
+
+def test_gga_decode_validate_length_fail():
+    sentence = "$GPGGA,152009.00,3652.48059177,N,07620.02018248,W,1,11,0.8,3.669,M,-34.579,M,,*57"
+    with pytest.raises(AssertionError):
+        ggaDecode(sentence, validate=True)
+
+
+def test_zda_dict2timestamp():
+    zda_dict = {
+        "hour": 11,
+        "min": 0,
+        "hsec": 0,
+        "sec": 3,
+        "mon": 3,
+        "year": 2006,
+        "day": 27,
+    }
+    result = zdaDict2TIMESTAMP(zda_dict)
+    assert result == "2006-03-27 11:00:03"