diff --git a/tests/test_airfoil.py b/tests/test_airfoil.py
new file mode 100644
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--- /dev/null
+++ b/tests/test_airfoil.py
@@ -0,0 +1,106 @@
+import pytest
+import numpy as np
+from build123d import Airfoil, Vector, Edge, Wire
+
+
+# --- parse_naca4 tests ------------------------------------------------------
+
+
+@pytest.mark.parametrize(
+    "code, expected",
+    [
+        ("2412", (0.02, 0.4, 0.12)),  # standard NACA 2412
+        ("0012", (0.0, 0.0, 0.12)),  # symmetric section
+        ("2213.323", (0.02, 0.2, 0.13323)),  # fractional thickness
+        ("NACA2412", (0.02, 0.4, 0.12)),  # with prefix
+    ],
+)
+def test_parse_naca4_variants(code, expected):
+    m, p, t = Airfoil.parse_naca4(code)
+    np.testing.assert_allclose([m, p, t], expected, rtol=1e-6)
+
+
+# --- basic construction tests -----------------------------------------------
+
+
+def test_airfoil_basic_construction():
+    airfoil = Airfoil("2412", n_points=40)
+    assert isinstance(airfoil, Airfoil)
+    assert isinstance(airfoil.camber_line, Edge)
+    assert isinstance(airfoil._camber_points, list)
+    assert all(isinstance(p, Vector) for p in airfoil._camber_points)
+
+    # Check metadata
+    assert airfoil.code == "2412"
+    assert pytest.approx(airfoil.max_camber, rel=1e-6) == 0.02
+    assert pytest.approx(airfoil.camber_pos, rel=1e-6) == 0.4
+    assert pytest.approx(airfoil.thickness, rel=1e-6) == 0.12
+    assert airfoil.finite_te is False
+
+
+def test_airfoil_finite_te_profile():
+    """Finite trailing edge version should have a line closing the profile."""
+    airfoil = Airfoil("2412", finite_te=True, n_points=40)
+    assert isinstance(airfoil, Wire)
+    assert airfoil.finite_te
+    assert len(list(airfoil.edges())) == 2
+
+
+def test_airfoil_infinite_te_profile():
+    """Infinite trailing edge (periodic spline)."""
+    airfoil = Airfoil("2412", finite_te=False, n_points=40)
+    assert isinstance(airfoil, Wire)
+    # Should contain a single closed Edge
+    assert len(airfoil.edges()) == 1
+    assert airfoil.edges()[0].is_closed
+
+
+# --- geometric / numerical validity -----------------------------------------
+
+
+def test_camber_line_geometry_monotonic():
+    """Camber x coordinates should increase monotonically along the chord."""
+    af = Airfoil("2412", n_points=80)
+    x_coords = [p.X for p in af._camber_points]
+    assert np.all(np.diff(x_coords) >= 0)
+
+
+def test_airfoil_chord_limits():
+    """Airfoil should be bounded between x=0 and x=1."""
+    af = Airfoil("2412", n_points=100)
+    all_points = af._camber_points
+    xs = np.array([p.X for p in all_points])
+    assert xs.min() >= -1e-9
+    assert xs.max() <= 1.0 + 1e-9
+
+
+def test_airfoil_thickness_scaling():
+    """Check that airfoil thickness scales linearly with NACA last two digits."""
+    af1 = Airfoil("0010", n_points=120)
+    af2 = Airfoil("0020", n_points=120)
+
+    # Extract main surface edge (for finite_te=False it's just one edge)
+    edge1 = af1.edges()[0]
+    edge2 = af2.edges()[0]
+
+    # Sample many points along each edge
+    n = 500
+    ys1 = [(edge1 @ u).Y for u in np.linspace(0.0, 1.0, n)]
+    ys2 = [(edge2 @ u).Y for u in np.linspace(0.0, 1.0, n)]
+
+    # Total height (max - min)
+    h1 = max(ys1) - min(ys1)
+    h2 = max(ys2) - min(ys2)
+
+    # For symmetric NACA 00xx, thickness is proportional to 't'
+    assert (h1 / h2) == pytest.approx(0.5, rel=0.05)
+
+
+def test_camber_line_is_centered():
+    """Mean of upper and lower surfaces should approximate camber line."""
+    af = Airfoil("2412", n_points=50)
+    # Extract central camber Y near mid-chord
+    mid_index = len(af._camber_points) // 2
+    mid_point = af._camber_points[mid_index]
+    # Camber line should be roughly symmetric around y=0 for small m
+    assert abs(mid_point.Y) < 0.05