added test for conversion of minus 180 degrees to radians

src/test/py/test_trigonometry.py

@@ -46,6 +46,12 @@ class MyTestCase(unittest.TestCase):
             delta *= -1
         self.assertLess(delta, 0.01)
 
+    def test_negative_180_deg_to_rad_should_be_negative_pi(self):
+        delta = deg2rad(-180) - -math.pi
+        if delta < 0:
+            delta *= -1
+        self.assertLess(delta, 0.01)
+
     def test_sin_0_should_be_0(self):
         self.assertEqual(sin_approx_bhaskara(0), 0)