Update test_grid.py (aimacode#448)

Author: antmarakis

tests/test_grid.py

@@ -18,5 +18,24 @@ def test_vector_clip():
     assert vector_clip((-1, 10), (0, 0), (9, 9)) == (0, 9)
 
 
+def test_turn_heading():
+	assert turn_heading((0, 1), 1) == (-1, 0)
+	assert turn_heading((0, 1), -1) == (1, 0)
+	assert turn_heading((1, 0), 1) == (0, 1)
+	assert turn_heading((1, 0), -1) == (0, -1)
+	assert turn_heading((0, -1), 1) == (1, 0)
+	assert turn_heading((0, -1), -1) == (-1, 0)
+	assert turn_heading((-1, 0), 1) == (0, -1)
+	assert turn_heading((-1, 0), -1) == (0, 1)
+
+
+def test_turn_left():
+	assert turn_left((0, 1)) == (-1, 0)
+
+
+def test_turn_right():
+	assert turn_right((0, 1)) == (1, 0)
+
+
 if __name__ == '__main__':
     pytest.main()