PW-567 add the old canvas formula

tests/lib/test_limits.py

@@ -0,0 +1,22 @@
+# coding=UTF-8
+
+import unittest2
+from api.lib.limits import calculate_canvas_limits, calculate_canvas_frame_limits
+
+
+class TestCalculate(unittest2.TestCase):
+
+    def test_calculate_canvas_limits(self):
+        self.assertEqual((100, 100), calculate_canvas_limits(100, 100))
+        self.assertEqual((500, 100), calculate_canvas_limits(800, 100))
+        self.assertEqual((100, 500), calculate_canvas_limits(100, 800))
+        self.assertEqual((20, 20), calculate_canvas_limits(10, 10))
+        self.assertEqual((150, 50), calculate_canvas_limits(
+            400, 50, True), "Framed canvas")
+
+    def test_calculate_canvas_frame_limits(self):
+        self.assertEqual((100, 100), calculate_canvas_frame_limits(100, 100))
+        self.assertEqual((40, 40), calculate_canvas_frame_limits(1, 1))
+        self.assertEqual((150, 150), calculate_canvas_frame_limits(200, 200))
+        self.assertEqual((150, 40), calculate_canvas_frame_limits(200, 10))
+        self.assertEqual((110, 120), calculate_canvas_frame_limits(112, 117), "round to nearest 10")