Debugging and Testing

Visual Studio debugger, breakpoints, unittest, and writing test cases.

Debugging in Visual Studio 2026

Visual Studio 2026 has a world-class Python debugger. Key techniques:

• Click the grey margin to the left of a line number to set a breakpoint (red dot).
• Press F5 to run. Execution pauses at breakpoints.
• F10 — Step Over (execute current line, don't enter function).
• F11 — Step Into (enter the function call).
• Shift+F11 — Step Out.
• Hover over any variable to see its current value in a tooltip.
• The Locals and Watch windows show all variables in scope.

Writing Tests with unittest

# calculator.py
def add(a, b): return a + b
def divide(a, b):
    if b == 0: raise ValueError("Cannot divide by zero")
    return a / b

# test_calculator.py
import unittest
from calculator import add, divide

class TestCalculator(unittest.TestCase):

    def test_add(self):
        self.assertEqual(add(3, 4), 7)
        self.assertEqual(add(-1, 1), 0)

    def test_divide(self):
        self.assertAlmostEqual(divide(10, 3), 3.333, places=2)

    def test_divide_by_zero(self):
        with self.assertRaises(ValueError):
            divide(5, 0)

if __name__ == "__main__":
    unittest.main()

Running Tests

In Visual Studio 2026, open the Test Explorer (Test → Test Explorer). It auto-discovers test files matching test_*.py and shows pass/fail for every test method.