Build out all 27 modules + capstone (#1)

Co-authored-by: claude <claude@jpaul.io>
Co-committed-by: claude <claude@jpaul.io>

modules/13-testing-in-the-ai-era/lab/solution/reference_test_tasks.py

@@ -0,0 +1,75 @@
+"""Reference test suite for the Module 13 lab. Peek only after you've tried it yourself.
+
+Named `reference_test_tasks.py` (not `test_*.py`) on purpose, so `python -m unittest discover`
+does NOT pick it up automatically. To run it directly from the tasks-app folder:
+
+    python -m unittest path/to/reference_test_tasks.py
+
+It assumes `tasks.py` is importable (run it from the tasks-app directory, or copy it there).
+
+The point of this file is to show the difference between a test that asserts CURRENT BEHAVIOR
+(a tautology that passes against the bug) and a test that encodes INTENT (and fails until the
+bug is fixed).
+"""
+
+import unittest
+
+from tasks import TaskList
+
+
+class TestTaskBasics(unittest.TestCase):
+    def test_add_appends_a_task(self):
+        tl = TaskList()
+        tl.add("write the tests")
+        self.assertEqual(len(tl.tasks), 1)
+        self.assertEqual(tl.tasks[0].title, "write the tests")
+        self.assertFalse(tl.tasks[0].done)
+
+    def test_complete_marks_done(self):
+        tl = TaskList()
+        tl.add("a")
+        tl.complete(0)
+        self.assertTrue(tl.tasks[0].done)
+
+    def test_pending_excludes_completed(self):
+        tl = TaskList()
+        tl.add("a")
+        tl.add("b")
+        tl.complete(0)
+        self.assertEqual([t.title for t in tl.pending()], ["b"])
+
+
+class TestPendingCount(unittest.TestCase):
+    def test_count_with_nothing_done_is_a_tautology(self):
+        # This passes even with the bug, because when nothing is completed
+        # "total" and "pending" are the same number. It proves almost nothing.
+        tl = TaskList()
+        tl.add("a")
+        tl.add("b")
+        self.assertEqual(tl.pending_count(), 2)
+
+    def test_count_reflects_intent_after_completing_one(self):
+        # This encodes what `count` is FOR: how many tasks are still pending.
+        # It FAILS against the planted bug (pending_count returns len(self.tasks)),
+        # and passes once pending_count returns len(self.pending()).
+        tl = TaskList()
+        tl.add("a")
+        tl.add("b")
+        tl.complete(0)
+        self.assertEqual(tl.pending_count(), 1)
+
+    def test_count_of_all_done_is_zero(self):
+        tl = TaskList()
+        tl.add("a")
+        tl.complete(0)
+        self.assertEqual(tl.pending_count(), 0)
+
+
+# The fix, for reference:
+#
+#     def pending_count(self) -> int:
+#         return len(self.pending())
+
+
+if __name__ == "__main__":
+    unittest.main()