diff --git a/wizard-work/beam/test_task_scheduler.py b/wizard-work/beam/test_task_scheduler.py
new file mode 100644
index 0000000..ec6049f
--- /dev/null
+++ b/wizard-work/beam/test_task_scheduler.py
@@ -0,0 +1,78 @@
+import random
+from task_scheduler import Task, makespan_exact, makespan_critical_path, _validate
+
+
+def test_empty():
+    assert makespan_exact([]) == 0
+    assert makespan_critical_path([]) == 0
+
+
+def test_single():
+    assert makespan_exact([Task("a", 5)]) == 5
+
+
+def test_chain():
+    assert makespan_exact([Task("a", 3), Task("b", 4, {"a"})]) == 7
+
+
+def test_parallel():
+    assert makespan_exact([Task("a", 3), Task("b", 4)]) == 4
+
+
+def test_diamond():
+    tasks = [Task("a", 3), Task("b", 4), Task("c", 2, {"a", "b"})]
+    assert makespan_exact(tasks) == 6
+    assert makespan_exact(tasks) == makespan_critical_path(tasks)
+
+
+def test_matches_critical_path_random():
+    random.seed(7)
+    for trial in range(500):
+        n = random.randint(0, 8)
+        tids = [f"t{i}" for i in range(n)]
+        tasks = []
+        for i, tid in enumerate(tids):
+            dur = random.randint(1, 6)
+            cand = tids[:i]
+            preds = set(random.sample(cand, random.randint(0, len(cand))))
+            tasks.append(Task(tid, dur, preds))
+        a = makespan_exact(tasks)
+        b = makespan_critical_path(tasks)
+        assert a == b
+
+
+def test_validation_duplicate():
+    try:
+        _validate([Task("a", 1), Task("a", 2)])
+    except ValueError:
+        return
+    raise AssertionError("expected ValueError")
+
+
+def test_validation_unknown_pred():
+    try:
+        _validate([Task("a", 1, {"z"})])
+    except ValueError:
+        return
+    raise AssertionError("expected ValueError")
+
+
+def test_validation_self():
+    try:
+        _validate([Task("a", 1, {"a"})])
+    except ValueError:
+        return
+    raise AssertionError("expected ValueError")
+
+
+def test_validation_cycle():
+    try:
+        _validate([Task("a", 1, {"b"}), Task("b", 1, {"a"})])
+    except ValueError:
+        return
+    raise AssertionError("expected ValueError")
+
+
+def test_zero_duration():
+    tasks = [Task("a", 0), Task("b", 2, {"a"})]
+    assert makespan_exact(tasks) == 2