[3.13] gh-151678: Add tests for tkinter.scrolledtext (GH-151753) (GH-151761)

Add a test for the ScrolledText widget, which had no tests: that it is
a Text widget held in a Frame with a Scrollbar, that Text methods work,
that the geometry manager methods are redirected to the frame while
configure is not, and that the scrollbar tracks the text view.
(cherry picked from commit a9db5cb52f)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Lib/test/test_tkinter/test_scrolledtext.py

@@ -0,0 +1,65 @@
+import unittest
+import tkinter
+from tkinter.scrolledtext import ScrolledText
+from test.support import requires
+from test.test_tkinter.support import setUpModule  # noqa: F401
+from test.test_tkinter.support import AbstractTkTest
+
+requires('gui')
+
+
+class ScrolledTextTest(AbstractTkTest, unittest.TestCase):
+
+    def create(self, **kwargs):
+        st = ScrolledText(self.root, **kwargs)
+        self.addCleanup(st.destroy)
+        return st
+
+    def test_create(self):
+        st = self.create(background='red', height=5)
+        # It is a Text widget held in a Frame together with a Scrollbar.
+        self.assertIsInstance(st, tkinter.Text)
+        self.assertIsInstance(st.frame, tkinter.Frame)
+        self.assertIsInstance(st.vbar, tkinter.Scrollbar)
+        self.assertEqual(st.winfo_parent(), str(st.frame))
+        # str() returns the frame, so that geometry managers manage it.
+        self.assertEqual(str(st), str(st.frame))
+        # Keyword options configure the Text.
+        self.assertEqual(str(st['background']), 'red')
+        self.assertEqual(st['height'], 5 if self.wantobjects else '5')
+
+    def test_text_methods(self):
+        st = self.create()
+        st.insert('1.0', 'hello\nworld')
+        self.assertEqual(st.get('1.0', 'end-1c'), 'hello\nworld')
+        self.assertEqual(st.index('end-1c'), '2.5')
+        st.delete('1.0', 'end')
+        self.assertEqual(st.get('1.0', 'end-1c'), '')
+
+    def test_geometry_methods(self):
+        st = self.create()
+        # configure is not redirected; it configures the Text.
+        st.configure(height=8)
+        self.assertEqual(st['height'], 8 if self.wantobjects else '8')
+        # Pack, Grid and Place methods are redirected to the frame.
+        st.pack()
+        self.root.update()
+        self.assertEqual(st.frame.winfo_manager(), 'pack')
+        self.assertEqual(st.pack_info(), st.frame.pack_info())
+        st.pack_forget()
+        self.assertEqual(st.frame.winfo_manager(), '')
+
+    def test_scrollbar(self):
+        st = self.create(height=5)
+        st.pack()
+        st.insert('1.0', '\n'.join(map(str, range(100))))
+        self.root.update()
+        # The scrollbar tracks the text view.
+        self.assertEqual(st.vbar.get(), st.yview())
+        st.yview_moveto(1.0)
+        self.root.update()
+        self.assertEqual(st.vbar.get()[1], 1.0)
+
+
+if __name__ == "__main__":
+    unittest.main()