Add a test that fish_exit handlers run on receipt of SIGHUP

tests/pexpects/exit_handlers.py

@@ -0,0 +1,33 @@
+#!/usr/bin/env python3
+from pexpect_helper import SpawnedProc
+import os
+import signal
+import tempfile
+from time import sleep
+
+# Ensure that on-exit handlers run even if we get SIGHUP.
+with tempfile.NamedTemporaryFile(mode="r", encoding="utf8") as tf:
+    sp = SpawnedProc()
+    fish_pid = sp.spawn.pid
+    sp.expect_prompt()
+    sp.sendline(
+        "function myexit --on-event fish_exit; /bin/echo $fish_pid > {filename}; end".format(
+            filename=tf.name
+        )
+    )
+    sp.expect_prompt()
+    os.kill(fish_pid, signal.SIGHUP)
+    # Note that fish's SIGHUP handling in interactive mode races with the call to select.
+    # So actually close its stdin, like a terminal emulator would do.
+    sp.spawn.close(force=False)
+    sp.spawn.wait()
+    tf.seek(0)
+    line = tf.readline().strip()
+    if line != str(fish_pid):
+        colors = sp.colors()
+        print(
+            """{RED}Failed to find pid written by exit handler{RESET}""".format(
+                **colors
+            )
+        )
+        print("""Expected '{}', found '{}'""".format(fish_pid, line))