Fix ResourceWarning from forked output streams

CHANGELOG.rst

@@ -1,3 +1,9 @@
+UNRELEASED
+==========
+
+* Fix unclosed stdout/stderr files created by forked worker
+  (`#106 <https://github.com/pytest-dev/pytest-forked/issues/106>`__).
+
 v1.7.5
 ======
 

src/pytest_forked/__init__.py

@@ -84,8 +84,11 @@ def _worker(runforked_fn, stdout_path, stderr_path, retval_path):
     os.close(stderr_fd)
 
     # redirect Python-level streams so print() etc. work
-    sys.stdout = open(stdout_path, "w", buffering=1)
-    sys.stderr = open(stderr_path, "w", buffering=1)
+    # keep handles to close below: capture swaps sys streams without closing
+    stdout_file = open(stdout_path, "w", buffering=1)
+    stderr_file = open(stderr_path, "w", buffering=1)
+    sys.stdout = stdout_file
+    sys.stderr = stderr_file
 
     try:
         retval = runforked_fn()
@@ -104,6 +107,11 @@ def _worker(runforked_fn, stdout_path, stderr_path, retval_path):
             sys.stderr.flush()
         except Exception:
             pass
+        for stream in (stdout_file, stderr_file):
+            try:
+                stream.close()
+            except Exception:
+                pass
 
     os._exit(0)
 

testing/test_boxed.py

@@ -116,6 +116,27 @@ def test_other_module():
     assert result.ret == 0
 
 
+@needsfork
+@pytest.mark.parametrize("capmode", ["fd", "sys"])
+def test_forked_no_unclosed_output_warning(testdir, capmode):
+    testdir.makeini("[pytest]\nfilterwarnings = error\n")
+    p1 = testdir.makepyfile(
+        """
+        import pytest
+
+        @pytest.mark.forked
+        def test_forked_pass():
+            assert True
+
+        def test_after_forked():
+            assert True
+    """
+    )
+    result = testdir.runpytest(p1, "--capture=%s" % capmode)
+    result.assert_outcomes(passed=2)
+    assert result.ret == 0
+
+
 def test_is_not_boxed_by_default(testdir):
     config = testdir.parseconfig(testdir.tmpdir)
     assert not config.option.forked