tests/conftest.py: add (disabled) checking for leaked fds in tests.

We don't actually fail if leaked fds are detected because several tests need
fixing first. But we do output a diagnostic.

Author: julian-smith-artifex-com

tests/conftest.py

@@ -1,4 +1,8 @@
+import os
+import platform
+
 import pymupdf
+
 import pytest
 
 @pytest.fixture(autouse=True)
@@ -7,10 +11,33 @@ def wrap(*args, **kwargs):
     Check that tests return with empty MuPDF warnings buffer. For example this
     detects failure to call fz_close_output() before fz_drop_output(), which
     (as of 2024-4-12) generates a warning from MuPDF.
+    
+    As of 2024-09-12 we also detect whether tests leave fds open; but for now
+    do not fail tests, because many tests need fixing.
     '''
     wt = pymupdf.TOOLS.mupdf_warnings()
     assert not wt, f'{wt=}'
     assert not pymupdf.TOOLS.set_small_glyph_heights()
+    next_fd_before = os.open(__file__, os.O_RDONLY)
+    os.close(next_fd_before)
+    
+    if platform.system() == 'Linux':
+        # Gather detailed information about leaked fds.
+        def get_fds():
+            import subprocess
+            path = 'PyMuPDF-linx-fds'
+            path_l = 'PyMuPDF-linx-fds-l'
+            command = f'ls /proc/{os.getpid()}/fd > {path}'
+            command_l = f'ls -l /proc/{os.getpid()}/fd > {path_l}'
+            subprocess.run(command, shell=1)
+            subprocess.run(command_l, shell=1)
+            with open(path) as f:
+                ret = f.read()
+                ret = ret.replace('\n', ' ')
+            with open(path_l) as f:
+                ret_l = f.read()
+            return ret, ret_l
+        open_fds_before, open_fds_before_l = get_fds()
 
     pymupdf._log_items_clear()
     pymupdf._log_items_active(True)
@@ -29,3 +56,23 @@ def wrap(*args, **kwargs):
 
     log_items = pymupdf._log_items()
     assert not log_items, f'log() was called; {len(log_items)=}.'
+    
+    if platform.system() == 'Linux':
+        # Show detailed information about leaked fds.
+        open_fds_after, open_fds_after_l = get_fds()
+        if open_fds_after != open_fds_before:
+            import textwrap
+            print(f'Test has changed process fds:')
+            print(f'    {open_fds_before=}')
+            print(f'     {open_fds_after=}')
+            print(f'open_fds_before_l:')
+            print(textwrap.indent(open_fds_before_l, '    '))
+            print(f'open_fds_after_l:')
+            print(textwrap.indent(open_fds_after_l, '    '))
+            #assert 0
+    
+    next_fd_after = os.open(__file__, os.O_RDONLY)
+    os.close(next_fd_after)
+    if next_fd_after != next_fd_before:
+        print(f'Test has leaked fds, {next_fd_before=} {next_fd_after=}. {args=} {kwargs=}.')
+        #assert 0, f'Test has leaked fds, {next_fd_before=} {next_fd_after=}. {args=} {kwargs=}.'