Let the next dictation start while the last one is still working

Pressing the shortcut while a transcript was being transcribed or cleaned up
did nothing, and the thought you had while waiting was lost. The microphone is
free the moment a recording stops, so the next dictation can now be spoken at
once; the pipeline queues it and each one is finished, pasted and reported in
the order it was spoken. The corner indicator stays with the recording under
way rather than being wiped by the previous run's progress, and a stop that
lands behind an unfinished run says it is waiting its turn.

tests/test_worker.py

@@ -8,6 +8,7 @@ afterwards. A pull request that reorders any of it shows up here.
 import contextlib
 import io
 import os
+import threading
 import unittest
 from unittest import mock
 
@@ -278,13 +279,41 @@ class Chain(DikteTest):
 
 
 class Busy(DikteTest):
-    def test_a_second_run_while_one_is_going_is_ignored(self):
+    def test_a_second_run_while_one_is_going_waits_its_turn(self):
+        """The microphone is free while a transcript is being cleaned up, so
+        the next dictation can already have been spoken by then. It has to run
+        once the first is done, in the order they were spoken, on one thread."""
         pipeline = worker.Pipeline(self.config())
-        pipeline._thread = mock.Mock(is_alive=lambda: True)
-        self.assertTrue(pipeline.busy)
-        with mock.patch.object(worker.threading, "Thread") as thread:
-            pipeline.run("/tmp/nope.wav", 1.0)
-        thread.assert_not_called()
+        order = []
+        started, gate = threading.Event(), threading.Event()
+
+        def work(wav_path, *_rest):
+            order.append(wav_path)
+            started.set()
+            if wav_path == "first.wav":
+                gate.wait(5)
+
+        with mock.patch.object(pipeline, "_work", side_effect=work):
+            pipeline.run("first.wav", 1.0)
+            self.assertTrue(started.wait(5))
+            pipeline.run("second.wav", 1.0)
+            # Held, not dropped and not running beside the first.
+            self.assertEqual(order, ["first.wav"])
+            gate.set()
+            pipeline._thread.join(5)
+        self.assertEqual(order, ["first.wav", "second.wav"])
+
+    def test_a_run_arriving_after_the_queue_drained(self):
+        """The worker thread ends with the queue; the next run brings one."""
+        pipeline = worker.Pipeline(self.config())
+        order = []
+        with mock.patch.object(pipeline, "_work",
+                               side_effect=lambda wav, *rest: order.append(wav)):
+            pipeline.run("first.wav", 1.0)
+            pipeline._thread.join(5)
+            pipeline.run("second.wav", 1.0)
+            pipeline._thread.join(5)
+        self.assertEqual(order, ["first.wav", "second.wav"])
 
     def test_the_chunk_length_matches_the_level_meter(self):
         """The silence thresholds are read in seconds, so the two must agree."""