gh-151678: Add tests for tkinter.scrolledtext (GH-151753)

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.

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

Author: serhiy-storchaka

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()