display_test: Add more extensive display.update tests

We have an interactive test, because there's no easy way to get
the screen pixels and see if the window only updates in the areas
given.

This is not perfect, because when running interactive the tests
run twice... once interactive, and once not. But it's still better
than repeating all the tests?

test/display_test.py

@@ -20,22 +20,6 @@ def setUp(self):
     def tearDown(self):
         display.quit()
 
-    def test_update(self):
-        """see if pygame.display.update takes rects with negative values.
-        "|Tags:display|"
-        """
-        screen = pygame.display.set_mode((100, 100))
-        screen.fill((55, 55, 55))
-
-        r1 = pygame.Rect(0, 0, 100, 100)
-        pygame.display.update(r1)
-
-        r2 = pygame.Rect(-10, 0, 100, 100)
-        pygame.display.update(r2)
-
-        r3 = pygame.Rect(-10, 0, -100, -100)
-        pygame.display.update(r3)
-
     def test_Info(self):
         inf = pygame.display.Info()
         self.assertNotEqual(inf.current_h, -1)
@@ -644,6 +628,112 @@ def test_toggle_fullscreen(self):
                 )
 
 
+class DisplayUpdateTest(unittest.TestCase):
+    def question(self, qstr):
+        """this is used in the interactive subclass."""
+
+    def setUp(self):
+        display.init()
+        self.screen = pygame.display.set_mode((500, 500))
+        self.screen.fill("black")
+        pygame.display.flip()
+        pygame.event.pump()  # so mac updates
+
+    def tearDown(self):
+        display.quit()
+
+    def test_update_negative(self):
+        """takes rects with negative values."""
+        self.screen.fill("green")
+
+        r1 = pygame.Rect(0, 0, 100, 100)
+        pygame.display.update(r1)
+
+        r2 = pygame.Rect(-10, 0, 100, 100)
+        pygame.display.update(r2)
+
+        r3 = pygame.Rect(-10, 0, -100, -100)
+        pygame.display.update(r3)
+
+        self.question("Is the screen green in (0, 0, 100, 100)?")
+
+    def test_update_sequence(self):
+        """only updates the part of the display given by the rects."""
+        self.screen.fill("green")
+        rects = [
+            pygame.Rect(0, 0, 100, 100),
+            pygame.Rect(100, 0, 100, 100),
+            pygame.Rect(200, 0, 100, 100),
+            pygame.Rect(300, 300, 100, 100),
+        ]
+        pygame.display.update(rects)
+        pygame.event.pump()  # so mac updates
+
+        self.question(f"Is the screen green in {rects}?")
+
+    def test_update_none_skipped(self):
+        """None is skipped inside sequences."""
+        self.screen.fill("green")
+        rects = (
+            None,
+            pygame.Rect(100, 0, 100, 100),
+            None,
+            pygame.Rect(200, 0, 100, 100),
+            pygame.Rect(300, 300, 100, 100),
+        )
+        pygame.display.update(rects)
+        pygame.event.pump()  # so mac updates
+
+        self.question(f"Is the screen green in {rects}?")
+
+    def test_update_none(self):
+        """does NOT update the display."""
+        self.screen.fill("green")
+        pygame.display.update(None)
+        pygame.event.pump()  # so mac updates
+        self.question(f"Is the screen black and NOT green?")
+
+    def test_update_no_args(self):
+        """does NOT update the display."""
+        self.screen.fill("green")
+        pygame.display.update()
+        pygame.event.pump()  # so mac updates
+        self.question(f"Is the WHOLE screen green?")
+
+    def test_update_args(self):
+        """updates the display using the args as a rect."""
+        self.screen.fill("green")
+        pygame.display.update(100, 100, 100, 100)
+        pygame.event.pump()  # so mac updates
+        self.question("Is the screen green in (100, 100, 100, 100)?")
+
+    def test_update_incorrect_args(self):
+        """raises a ValueError when inputs are wrong."""
+
+        with self.assertRaises(ValueError):
+            pygame.display.update(100, "asdf", 100, 100)
+
+        with self.assertRaises(ValueError):
+            pygame.display.update([100, "asdf", 100, 100])
+
+    def test_update_no_init(self):
+        """raises a pygame.error."""
+
+        pygame.display.quit()
+        with self.assertRaises(pygame.error):
+            pygame.display.update()
+
+
+class DisplayUpdateInteractiveTest(DisplayUpdateTest):
+    """Because we want these tests to run as interactive and not interactive."""
+
+    __tags__ = ["interactive"]
+
+    def question(self, qstr):
+        """since this is the interactive sublcass we ask a question."""
+        question(qstr)
+
+
 class DisplayInteractiveTest(unittest.TestCase):
 
     __tags__ = ["interactive"]