Make the simulator reproducible and widen the burst tests

A transmitter seeded itself from the builtin hash() of its label, and that
is salted per interpreter, so every run produced different synthetic
speech and keying. A test that failed could not be made to fail again --
the one thing needed to fix it. crc32 gives the same content every run.

The hang test then compounded it by listening for a 1 s burst in a 6 s
cycle over three sweeps: it is the release after the transmission that is
under test, but a missed burst failed it just the same, with "nothing
recorded". Now 2 s in 5 s over six sweeps, so only the ending can fail it.

The neighbouring test had the opposite fault: asserting only that nothing
was truncated, it passed whether or not the burst was ever heard. It now
requires the recording it is drawing a conclusion from.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

bandsaunter/simulator.py

@@ -10,6 +10,7 @@ from __future__ import annotations
 
 import math
 import time
+import zlib
 from dataclasses import dataclass, field
 
 import numpy as np
@@ -115,7 +116,11 @@ class VirtualTransmitter:
     _rng: np.random.Generator = field(default=None, init=False, repr=False)
 
     def __post_init__(self):
-        self._seed = abs(hash(self.label or self.frequency)) % 2**31
+        # crc32 rather than hash(): the builtin is salted per interpreter, so
+        # a test's synthetic speech and keying differed on every run and a
+        # failure could not be reproduced by running it again.
+        key = str(self.label or self.frequency).encode()
+        self._seed = zlib.crc32(key)
         self._rng = np.random.default_rng(self._seed)
         if not self.label:
             self.label = f"{self.frequency/1e6:.4f} MHz {self.mode}"

tests/test_scanner.py

@@ -52,11 +52,16 @@ def test_record_seconds_is_honoured_exactly(tmp_path):
 
 
 def test_hang_seconds_ends_a_finished_transmission(tmp_path):
-    """A transmitter that stops must release the scanner after the hang time."""
+    """A transmitter that stops must release the scanner after the hang time.
+
+    What is under test is the ending, not the catching, so the burst is a
+    generous 40% of the cycle over six sweeps: landing on it is meant to be
+    easy, and only the release afterwards should be able to fail this.
+    """
     tx = [V(146_520_000, "nfm", 0.4, 12_500, "burst",
-            period_seconds=6.0, on_seconds=1.0)]
+            period_seconds=5.0, on_seconds=2.0)]
     s, hits = run_scan(tmp_path, tx, "146.4M-146.6M",
-                       record_seconds=20.0, hang_seconds=0.8, max_cycles=3)
+                       record_seconds=20.0, hang_seconds=0.8, max_cycles=6)
     assert hits, "nothing recorded"
     ended_on_silence = [h for h in hits if "quiet" in h.stop_reason]
     assert ended_on_silence, [h.stop_reason for h in hits]
@@ -369,9 +374,12 @@ def test_being_cut_off_mid_transmission_is_reported(tmp_path):
 
 def test_no_warning_when_the_signal_really_ended(tmp_path):
     tx = [V(146_520_000, "nfm", 0.4, 12_500, "burst",
-            period_seconds=12.0, on_seconds=2.0)]
+            period_seconds=5.0, on_seconds=2.0)]
     s, hits = run_scan(tmp_path, tx, "146.4M-146.6M", record_seconds=20.0,
-                       hang_seconds=1.0, max_cycles=3, revisit_seconds=0.1)
+                       hang_seconds=1.0, max_cycles=6, revisit_seconds=0.1)
+    # Without a recording there is nothing to warn about either way, so the
+    # count alone would pass whether or not the burst was ever heard.
+    assert hits, "nothing recorded"
     assert s.stats.truncated == 0