fix: save coverage data on SIGTERM (#1600)

* Add test that reproduces the issue

* Suggested fix - always save data in sigterm exit flow

* Address test failures on MacOS due to lack of 'Terminated' output on SIGTERM

coverage/control.py

@@ -653,7 +653,7 @@ def _atexit(self, event: str = "atexit") -> None:
             self._debug.write(f"{event}: pid: {os.getpid()}, instance: {self!r}")
         if self._started:
             self.stop()
-        if self._auto_save:
+        if self._auto_save or event == "sigterm":
             self.save()
 
     def _on_sigterm(self, signum_unused: int, frame_unused: Optional[FrameType]) -> None:

tests/test_concurrency.py

@@ -705,7 +705,7 @@ class SigtermTest(CoverageTest):
     """Tests of our handling of SIGTERM."""
 
     @pytest.mark.parametrize("sigterm", [False, True])
-    def test_sigterm_saves_data(self, sigterm: bool) -> None:
+    def test_sigterm_multiprocessing_saves_data(self, sigterm: bool) -> None:
         # A terminated process should save its coverage data.
         self.make_file("clobbered.py", """\
             import multiprocessing
@@ -751,6 +751,31 @@ def subproc(x):
             expected = "clobbered.py 17 5 71% 5-10"
         assert self.squeezed_lines(out)[2] == expected
 
+    def test_sigterm_threading_saves_data(self) -> None:
+        # A terminated process should save its coverage data.
+        self.make_file("handler.py", """\
+            import os, signal
+
+            print("START", flush=True)
+            print("SIGTERM", flush=True)
+            os.kill(os.getpid(), signal.SIGTERM)
+            print("NOT HERE", flush=True)
+            """)
+        self.make_file(".coveragerc", """\
+            [run]
+            # The default concurrency option.
+            concurrency = thread
+            sigterm = true
+            """)
+        out = self.run_command("coverage run handler.py")
+        if env.LINUX:
+            assert out == "START\nSIGTERM\nTerminated\n"
+        else:
+            assert out == "START\nSIGTERM\n"
+        out = self.run_command("coverage report -m")
+        expected = "handler.py 5 1 80% 6"
+        assert self.squeezed_lines(out)[2] == expected
+
     def test_sigterm_still_runs(self) -> None:
         # A terminated process still runs its own SIGTERM handler.
         self.make_file("handler.py", """\