start with code slightly adapted from htest fake widget class containing yview only fake event class type delta num amount start with code slightly adapted from htest fake widget class containing yview only fake event class type delta num amount
"Test tree. coverage 56%."

from idlelib import tree
import unittest
from test.support import requires
requires('gui')
from tkinter import Tk, EventType, SCROLL


class TreeTest(unittest.TestCase):

    @classmethod
    def setUpClass(cls):
        cls.root = Tk()
        cls.root.withdraw()

    @classmethod
    def tearDownClass(cls):
        cls.root.destroy()
        del cls.root

    def test_init(self):
        
        sc = tree.ScrolledCanvas(
            self.root, bg="white", highlightthickness=0, takefocus=1)
        sc.frame.pack(expand=1, fill="both", side='left')
        item = tree.FileTreeItem(tree.ICONDIR)
        node = tree.TreeNode(sc.canvas, None, item)
        node.expand()


class TestScrollEvent(unittest.TestCase):

    def test_wheel_event(self):
        
        class _Widget:
            def __init__(widget, *expected):
                widget.expected = expected
            def yview(widget, *args):
                self.assertTupleEqual(widget.expected, args)
        
        class _Event:
            pass
        
        tests = ((EventType.MouseWheel, 120, -1, -5),
                 (EventType.MouseWheel, -120, -1, 5),
                 (EventType.ButtonPress, -1, 4, -5),
                 (EventType.ButtonPress, -1, 5, 5))

        event = _Event()
        for ty, delta, num, amount in tests:
            event.type = ty
            event.delta = delta
            event.num = num
            res = tree.wheel_event(event, _Widget(SCROLL, amount, "units"))
            self.assertEqual(res, "break")


if __name__ == '__main__':
    unittest.main(verbosity=2)