test: increase spawn test child timeout to 30 seconds

Example CI failure:

  3/157 Test   #3: mptest ...............................***Failed    1.06 sec
[ TEST ] spawn_tests.cpp:44: SpawnProcess does not run callback in child
./ipc/libmultiprocess/test/mp/test/spawn_tests.cpp:108: failed: expected exited; Timeout waiting for child process to exit
stack: bf2ed1 cc4091 cc4545 d817f9 d82ba3 bf220b ee33f4b9 ee33f555
./ipc/libmultiprocess/test/mp/test/spawn_tests.cpp:109: failed: expected WIFEXITED(status) && WEXITSTATUS(status) == 0
stack: bf2e03 cc4091 cc4545 d817f9 d82ba3 bf220b ee33f4b9 ee33f555
[ FAIL ] spawn_tests.cpp:44: SpawnProcess does not run callback in child (1051610 μs)
[ TEST ] test.cpp:124: Call FooInterface methods
[ PASS ] test.cpp:124: Call FooInterface methods (3744 μs)
[ TEST ] test.cpp:216: Call IPC method after client connection is closed
[ PASS ] test.cpp:216: Call IPC method after client connection is closed (363 μs)
[ TEST ] test.cpp:233: Calling IPC method after server connection is closed
[ PASS ] test.cpp:233: Calling IPC method after server connection is closed (346 μs)
[ TEST ] test.cpp:250: Calling IPC method and disconnecting during the call
[ PASS ] test.cpp:250: Calling IPC method and disconnecting during the call (354 μs)
[ TEST ] test.cpp:270: Calling IPC method, disconnecting and blocking during the call
[ PASS ] test.cpp:270: Calling IPC method, disconnecting and blocking during the call (554 μs)
[ TEST ] test.cpp:319: Make simultaneous IPC calls on single remote thread
[ PASS ] test.cpp:319: Make simultaneous IPC calls on single remote thread (741 μs)
6 test(s) passed
1 test(s) failed

Fixes bitcoin/bitcoin#34975

Author: Sjors

test/mp/test/spawn_tests.cpp

@@ -20,6 +20,8 @@
 
 namespace {
 
+constexpr auto FAILURE_TIMEOUT = std::chrono::seconds{30};
+
 // Poll for child process exit using waitpid(..., WNOHANG) until the child exits
 // or timeout expires. Returns true if the child exited and status_out was set.
 // Returns false on timeout or error.
@@ -94,9 +96,9 @@ KJ_TEST("SpawnProcess does not run callback in child")
     ::close(fd);
 
     int status{0};
-    // Give the child up to 1 second to exit. If it does not, terminate it and
+    // Give the child some time to exit. If it does not, terminate it and
     // reap it to avoid leaving a zombie behind.
-    const bool exited{WaitPidWithTimeout(pid, std::chrono::milliseconds{1000}, status)};
+    const bool exited{WaitPidWithTimeout(pid, FAILURE_TIMEOUT, status)};
     if (!exited) {
         ::kill(pid, SIGKILL);
         ::waitpid(pid, &status, /*options=*/0);