tests: Fix unclosed file in fd_check script

docs/changelog.rst

@@ -25,6 +25,7 @@ In progress (unreleased)
 * :gh:issue:`1111` :mod:`mitogen`: Replace uses of deprecated
   :py:func:`pkgutil.find_loader`
 * :gh:issue:`1213` :mod:`mitogen`: Fix unclosed file in first stage
+* :gh:issue:`1213` tests: Fix unclosed file in fd_check script
 
 
 v0.3.21 (2025-01-20)

tests/data/fd_check.py

@@ -26,6 +26,7 @@ def controlling_tty():
         return None
 
 
+out_path = sys.argv[1]
 fd = int(sys.argv[2])
 st = os.fstat(fd)
 
@@ -35,7 +36,7 @@ if sys.argv[3] == 'write':
 else:
     buf = os.read(fd, 4).decode()
 
-open(sys.argv[1], 'w').write(repr({
+output = repr({
     'buf': buf,
     'flags': fcntl.fcntl(fd, fcntl.F_GETFL),
     'st_mode': st.st_mode,
@@ -43,4 +44,21 @@ open(sys.argv[1], 'w').write(repr({
     'st_ino': st.st_ino,
     'ttyname': ttyname(fd),
     'controlling_tty': controlling_tty(),
-}))
+})
+
+try:
+    out_f = open(out_path, 'w')
+except Exception:
+    exc = sys.exc_info()[1]
+    sys.stderr.write("Failed to open %r: %r" % (out_path, exc))
+    sys.exit(1)
+
+try:
+    out_f.write(output)
+except Exception:
+    out_f.close()
+    exc = sys.exc_info()[1]
+    sys.stderr.write("Failed to write to %r: %r" % (out_path, exc))
+    sys.exit(2)
+
+out_f.close()