test: deflake test_signal_forwarding by waiting for handler installation (#6113)

Author: baszalmstra

tests/data/run_signals/test.py

@@ -9,6 +9,10 @@
 if output_file.exists():
     output_file.unlink()
 
+ready_file = Path("ready.txt")
+if ready_file.exists():
+    ready_file.unlink()
+
 
 def signal_handler(signum, frame):
     output_file.write_text(f"Signal handler called with signal {signum}\n")
@@ -20,6 +24,11 @@ def signal_handler(signum, frame):
 
 signal.signal(signal.SIGINT, signal_handler)
 
+# Signal to the test driver that the SIGINT handler is now installed. Without
+# this, the driver might deliver SIGINT before this line is reached, in which
+# case the default handler kills Python with exit code 130.
+ready_file.write_text("ready\n")
+
 while True:
     print("Running...\n")
     time.sleep(1)

tests/integration_python/test_run_cli.py

@@ -1694,7 +1694,21 @@ def test_signal_forwarding(pixi: Path, tmp_pixi_workspace: Path) -> None:
         [pixi, "run", "--manifest-path", manifest, "start"], cwd=tmp_data_path
     )
 
-    time.sleep(1)  # wait for the process to start
+    # Wait for the child to install its SIGINT handler. Sleeping a fixed
+    # interval here is flaky on slower runners (notably macOS-aarch64): if the
+    # signal arrives before Python registers the handler, the default action
+    # kills the process with exit code 130 (128 + SIGINT).
+    ready_file = tmp_data_path.joinpath("ready.txt")
+    deadline = time.monotonic() + 30
+    while not ready_file.exists():
+        if process.poll() is not None:
+            raise AssertionError(
+                f"pixi exited before the task became ready (code {process.returncode})"
+            )
+        if time.monotonic() > deadline:
+            process.kill()
+            raise AssertionError("Timed out waiting for the task to install its SIGINT handler")
+        time.sleep(0.1)
 
     # send a SIGINT to the process
     process.send_signal(signal.SIGINT)