[utils] canonicalize rotation matrices before caching

masque/test/test_utils.py

@@ -89,6 +89,23 @@ def test_rotation_matrix_non_manhattan() -> None:
     assert_allclose(m, [[s, -s], [s, s]], atol=1e-10)
 
 
+def test_rotation_matrix_canonicalizes_before_caching() -> None:
+    expected = rotation_matrix_2d(pi / 2)
+
+    for angle in (pi / 2 + 1e-12, pi / 2 - 1e-12, -3 * pi / 2, 5 * pi / 2):
+        assert rotation_matrix_2d(angle) is expected
+
+    assert not expected.flags.writeable
+
+
+def test_rotation_matrix_does_not_snap_non_manhattan_angle() -> None:
+    cardinal = rotation_matrix_2d(pi / 2)
+    nearby = rotation_matrix_2d(pi / 2 + 2e-3)
+
+    assert nearby is not cardinal
+    assert not numpy.array_equal(nearby, cardinal)
+
+
 def test_apply_transforms() -> None:
     # cumulative [x_offset, y_offset, rotation (rad), mirror_x (0 or 1)]
     t1 = [10, 20, 0, 0]