Rename test to tests; fix equator length.

tests/test_vector.py

@@ -0,0 +1,28 @@
+"""
+Test vector operations.
+"""
+import numpy as np
+
+from roentgen.vector import compute_angle, turn_by_angle
+
+__author__ = "Sergey Vartanov"
+__email__ = "me@enzet.ru"
+
+ROOT: float = np.sqrt(2)
+
+
+def test_compute_angle() -> None:
+    """Test angle computing for all angles between 0 and 2π with step π / 4."""
+    assert np.allclose(compute_angle((1, 0)), 0)
+    assert np.allclose(compute_angle((ROOT, ROOT)), np.pi * 0.25)
+    assert np.allclose(compute_angle((0, 1)), np.pi * 0.5)
+    assert np.allclose(compute_angle((-ROOT, ROOT)), np.pi * 0.75)
+    assert np.allclose(compute_angle((-1, 0)), np.pi)
+    assert np.allclose(compute_angle((-ROOT, -ROOT)), np.pi * 1.25)
+    assert np.allclose(compute_angle((0, -1)), np.pi * 1.5)
+    assert np.allclose(compute_angle((ROOT, -ROOT)), np.pi * 1.75)
+
+
+def test_turn_by_compute_angle() -> None:
+    """Test turing one angle by another."""
+    assert np.allclose(turn_by_angle((1, 0), np.pi / 2), np.array((0, 1)))