tests: Fix broken SIGINT test

The old test would send the interrupt signal before the script had
a chance to enter the integration loop, and thus the custom signal
handler was never tested. The new version waits for the subprocess
to write it's ready for the interrupt signal, and the traceback is
checked to confirm the signal was re-raised by the script interface.

testsuite/python/sigint.py

@@ -22,19 +22,55 @@
 import time
 import sys
 import pathlib
+import os
 
 
 class SigintTest(ut.TestCase):
 
-    def setUp(self):
-        script = str(pathlib.Path(__file__).parent / 'sigint_child.py')
-        self.process = subprocess.Popen([sys.executable, script])
+    script = str(pathlib.Path(__file__).parent / 'sigint_child.py')
+
+    def check_signal_handling(self, process, sig):
+        # send signal
+        process.send_signal(sig)
+        # capture stderr and return code (negative of signum)
+        stdout, stderr = process.communicate(input=None, timeout=6.)
+        assert stdout is None
+        traceback = stderr.decode()
+        return_code = process.poll()
+        signum = -return_code
+        self.assertEqual(signum, sig.value)
+        if sig == signal.Signals.SIGTERM:
+            self.assertEqual(traceback, "")
+        elif sig == signal.Signals.SIGINT:
+            self.assertIn(" self.integrator.run(", traceback)
+            self.assertTrue(traceback.endswith(
+                " in handle_sigint\n    signal.raise_signal(signal.Signals.SIGINT)\nKeyboardInterrupt\n"))
 
     def test_signal_handling(self):
-        self.process.send_signal(signal.Signals.SIGINT)
-        # Wait for the signal to arrive and one integration step to be finished
-        time.sleep(1)
-        self.assertIsNotNone(self.process.poll())
+        signals = [signal.Signals.SIGINT, signal.Signals.SIGTERM]
+        processes = []
+        # open asynchronous processes with non-blocking read access on stderr
+        for _ in range(len(signals)):
+            process = subprocess.Popen([sys.executable, self.script],
+                                       stderr=subprocess.PIPE)
+            os.set_blocking(process.stderr.fileno(), False)
+            processes.append(process)
+
+        # wait for the script to reach the integration loop
+        time.sleep(0.5)
+        for process, sig in zip(processes, signals):
+            tick = time.time()
+            while True:
+                message = process.stderr.readline().decode()
+                if message == "start of integration loop\n":
+                    # wait for the script to enter the integrator run method
+                    time.sleep(0.1)
+                    # send signal and check process behavior
+                    self.check_signal_handling(process, sig)
+                    break
+                tock = time.time()
+                assert tock - tick < 8., "subprocess timed out"
+                time.sleep(0.1)
 
 
 if __name__ == '__main__':

testsuite/python/sigint_child.py

@@ -16,6 +16,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
+import sys
 import numpy as np
 import espressomd
 
@@ -26,5 +27,6 @@
 for i in range(100):
     system.part.add(pos=np.random.random() * system.box_l)
 
+print("start of integration loop", file=sys.stderr)
 while True:
-    system.integrator.run(1000)
+    system.integrator.run(100000)