Add trade ledger debugging exercise

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test_ledger.py

@@ -0,0 +1,98 @@
+import io
+import unittest
+
+from ledger import Ledger, Trade
+from logger import BufferedLogger
+
+
+def make_ledger(level="INFO"):
+    out = io.StringIO()
+    log = BufferedLogger("test", level=level, stream=out, capacity=1000)
+    return Ledger(log), log, out
+
+
+class PositionTests(unittest.TestCase):
+    def test_buys_average_in(self):
+        ledger, _, _ = make_ledger()
+        ledger.apply(Trade("T1", "AAPL", "BUY", 100, 100.0))
+        ledger.apply(Trade("T2", "AAPL", "BUY", 100, 110.0))
+        pos = ledger.position("AAPL")
+        self.assertEqual(pos.qty, 200)
+        self.assertAlmostEqual(pos.avg_price, 105.0)
+
+    def test_partial_sell_realizes_pnl(self):
+        ledger, _, _ = make_ledger()
+        ledger.apply(Trade("T1", "AAPL", "BUY", 100, 100.0))
+        ledger.apply(Trade("T2", "AAPL", "SELL", 40, 110.0))
+        pos = ledger.position("AAPL")
+        self.assertEqual(pos.qty, 60)
+        self.assertAlmostEqual(pos.avg_price, 100.0)
+        self.assertAlmostEqual(pos.realized, 400.0)
+
+    def test_close_out(self):
+        ledger, _, _ = make_ledger()
+        ledger.apply(Trade("T1", "AAPL", "BUY", 100, 100.0))
+        ledger.apply(Trade("T2", "AAPL", "SELL", 100, 90.0))
+        pos = ledger.position("AAPL")
+        self.assertEqual(pos.qty, 0)
+        self.assertAlmostEqual(pos.realized, -1000.0)
+
+    def test_position_flip(self):
+        ledger, _, _ = make_ledger()
+        ledger.apply(Trade("T1", "AAPL", "BUY", 100, 100.0))
+        ledger.apply(Trade("T2", "AAPL", "SELL", 150, 105.0))
+        pos = ledger.position("AAPL")
+        self.assertEqual(pos.qty, -50)
+        self.assertAlmostEqual(pos.realized, 500.0)
+        self.assertTrue(pos.avg_price, 105.0)
+
+
+class ValidationTests(unittest.TestCase):
+    def test_zero_qty_rejected(self):
+        ledger, _, _ = make_ledger()
+        with self.assertRaises(ValueError):
+            ledger.apply(Trade("T1", "AAPL", "BUY", 0, 100.0))
+
+    def test_rejection_is_logged(self):
+        ledger, log, out = make_ledger()
+        with self.assertRaises(ValueError):
+            ledger.apply(Trade("T9", "AAPL", "BUY", 0, 100.0))
+        log.flush()
+        for line in out.getvalue().splitlines():
+            if "ERROR" in line:
+                self.assertIn("trade_id=T9", line)
+
+
+class LoggerTests(unittest.TestCase):
+    def test_info_written(self):
+        ledger, log, out = make_ledger()
+        ledger.apply(Trade("T1", "AAPL", "BUY", 10, 100.0))
+        log.flush()
+        self.assertIn("applied BUY 10@100.00", out.getvalue())
+
+    def test_debug_suppressed(self):
+        _, log, out = make_ledger()
+        log.debug("noisy")
+        log.flush()
+        self.assertNotIn("noisy", out.getvalue())
+
+    def test_context_attached(self):
+        ledger, log, out = make_ledger()
+        ledger.apply(Trade("T1", "AAPL", "BUY", 10, 100.0))
+        log.flush()
+        self.assertIn("trade_id=T1", out.getvalue())
+        self.assertIn("symbol=AAPL", out.getvalue())
+
+
+class RebuildTests(unittest.TestCase):
+    def test_rebuild_matches_live(self):
+        ledger, _, _ = make_ledger()
+        ledger.apply(Trade("T1", "AAPL", "BUY", 100, 100.0))
+        ledger.apply(Trade("T2", "MSFT", "BUY", 50, 400.0))
+        ledger.apply(Trade("T3", "AAPL", "BUY", 20, 101.0))
+        rebuilt = Ledger.rebuild(ledger.history, BufferedLogger("eod", stream=io.StringIO()))
+        self.assertEqual(ledger.reconcile(rebuilt), [])
+
+
+if __name__ == "__main__":
+    unittest.main()