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/CMakeLists.txt

@@ -23,7 +23,11 @@
 
   Configure a python test case.
 
-  Flag arguments: none.
+  Flag arguments:
+
+  * ``NO_MPI``: run test case without MPI, i.e. in singleton mode. Only use
+    this option when relevant to the test, e.g. to check signal propagation
+    (MPI vendors introduce their own implementation-defined signal handlers).
 
   Single-value arguments:
 
@@ -50,7 +54,7 @@
 
 #]=======================================================================]
 function(python_test)
-  cmake_parse_arguments(TEST "" "FILE;MAX_NUM_PROC;GPU_SLOTS;SUFFIX"
+  cmake_parse_arguments(TEST "NO_MPI" "FILE;MAX_NUM_PROC;GPU_SLOTS;SUFFIX"
                         "DEPENDS;DEPENDENCIES;LABELS;ARGUMENTS" ${ARGN})
   get_filename_component(TEST_NAME ${TEST_FILE} NAME_WE)
   set(TEST_FILE_CONFIGURED "${CMAKE_CURRENT_BINARY_DIR}/${TEST_NAME}.py")
@@ -65,7 +69,13 @@ function(python_test)
   set(TEST_FILE ${TEST_FILE_CONFIGURED})
 
   if(NOT DEFINED TEST_MAX_NUM_PROC)
-    set(TEST_MAX_NUM_PROC 4)
+    if(${TEST_NO_MPI})
+      set(TEST_MAX_NUM_PROC 1)
+    else()
+      set(TEST_MAX_NUM_PROC 4)
+    endif()
+  elseif(${TEST_NO_MPI} AND NOT ${TEST_MAX_NUM_PROC} EQUAL 1)
+    message(FATAL_ERROR "NO_MPI and MAX_NUM_PROC are mutually exclusive")
   endif()
   if(NOT DEFINED TEST_GPU_SLOTS)
     set(TEST_GPU_SLOTS 0)
@@ -77,7 +87,7 @@ function(python_test)
     set(TEST_NUM_PROC ${TEST_MAX_NUM_PROC})
   endif()
 
-  if(EXISTS ${MPIEXEC})
+  if(EXISTS ${MPIEXEC} AND NOT ${TEST_NO_MPI})
     espresso_set_mpiexec_tmpdir(${TEST_NAME})
     add_test(
       NAME ${TEST_NAME}
@@ -352,7 +362,7 @@ python_test(FILE lb_momentum_conservation.py MAX_NUM_PROC 1 GPU_SLOTS 1 SUFFIX
             1_core)
 python_test(FILE p3m_electrostatic_pressure.py MAX_NUM_PROC 2 GPU_SLOTS 1)
 python_test(FILE p3m_madelung.py MAX_NUM_PROC 2 GPU_SLOTS 2 LABELS long)
-python_test(FILE sigint.py DEPENDENCIES sigint_child.py MAX_NUM_PROC 1)
+python_test(FILE sigint.py DEPENDENCIES sigint_child.py NO_MPI)
 python_test(FILE lb_density.py MAX_NUM_PROC 1)
 python_test(FILE observable_chain.py MAX_NUM_PROC 4)
 python_test(FILE mpiio.py MAX_NUM_PROC 4)

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)