"""
Unit tests for the compute_moment_of_inertia function.
Tests cover:
- Correct computation for simple polygons (square)
- Handling of MultiPolygon geometries
- Zero and negative weight values
- Invalid geometry type validation
- Area scaling consistency
- Mass distribution in composite geometries
"""
# Copyright 2025 Institute of Light and Matter, CNRS UMR 5306, University Claude Bernard Lyon 1
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import math
import pytest
from shapely.geometry import MultiPolygon, Polygon
from configuration.utils.functions import compute_moment_of_inertia
[docs]
def test_square_polygon() -> None:
"""Test moment of inertia for a unit square at origin."""
square = Polygon([(0, 0), (1, 0), (1, 1), (0, 1)]) # cm
weight = 2.0
result = compute_moment_of_inertia(square, weight)
# Analytical: I = (m/6) for unit square about centroid (converted to kg·m² as per function)
expected = (weight / 6.0) * 1e-4
print(f"Square moment of inertia: {result}, expected: {expected}")
assert math.isclose(result, expected, rel_tol=1e-6)
[docs]
def test_multipolygon_sum() -> None:
"""Test that MultiPolygon sums the moments of the components."""
poly1 = Polygon([(0, 0), (1, 0), (1, 1), (0, 1)])
poly2 = Polygon([(2, 0), (3, 0), (3, 1), (2, 1)])
mp = MultiPolygon([poly1, poly2])
weight = 4.0
# Should be the same as two squares, each with half the weight
expected = compute_moment_of_inertia(poly1, weight / 2) + compute_moment_of_inertia(poly2, weight / 2)
result = compute_moment_of_inertia(mp, weight)
assert math.isclose(result, expected, rel_tol=1e-8)
[docs]
def test_zero_weight() -> None:
"""Test that zero weight returns zero moment."""
square = Polygon([(0, 0), (1, 0), (1, 1), (0, 1)])
assert compute_moment_of_inertia(square, 0.0) == 0.0
[docs]
def test_negative_weight() -> None:
"""Test that negative weight returns negative moment."""
square = Polygon([(0, 0), (1, 0), (1, 1), (0, 1)])
result = compute_moment_of_inertia(square, -2.0)
assert result < 0
[docs]
def test_invalid_geometry_type() -> None:
"""Test that invalid geometry raises TypeError."""
with pytest.raises(TypeError):
compute_moment_of_inertia("not_a_polygon", 1.0)
[docs]
def test_scaling_with_area() -> None:
"""Test that scaling the polygon scales the moment of inertia by area^2."""
square = Polygon([(0, 0), (1, 0), (1, 1), (0, 1)])
weight = 2.0
I1 = compute_moment_of_inertia(square, weight)
# If distance scaled by 2, mass scaled by 4 then inertia should be scaled by 16 (since inertia ~ mass * r^2)
square2 = Polygon([(0, 0), (2, 0), (2, 2), (0, 2)])
I2 = compute_moment_of_inertia(square2, weight * 4)
assert math.isclose(I2, I1 * 16, rel_tol=1e-6)