test: [_determine_margin] add TTA._STRATEGY.PERCENT unit tests

Test _determine_margin() with margins specified as percentage

test/test_adjusters.py

@@ -74,3 +74,20 @@ class TestTargetTimeAdjuster(unittest.TestCase):
             # test
             for time, margin, expected in test_cases:
                 self.assertEqual(tta._determine_margin(time, margin, strategy), expected)
+
+        with self.subTest("PERCENT"):
+            strategy = adjusters.TargetTimeAdjuster._STRATEGY.PERCENT
+            test_cases = []
+            # populate test cases with tuples of (time, margin, expected) as above
+            # zero margin
+            test_cases.append((60.0, 0.0, (60.0, 60.0)))
+            # margin of 5.0
+            test_cases.append((60.0, 5.0, (57.0, 63.0)))
+            # margin of 10.0
+            test_cases.append((60.0, 10.0, (54.0, 66.0)))
+            # margin of 100.0
+            test_cases.append((60.0, 100.0, (0.0, 120.0)))
+
+            # test
+            for time, margin, expected in test_cases:
+                self.assertEqual(tta._determine_margin(time, margin, strategy), expected)