add test for chdir("/") behaviour

tests/cwd_test.py

@@ -0,0 +1,20 @@
+import os
+from subprocess import run, PIPE
+
+import pytest
+
+@pytest.mark.usefixtures('both_debug_modes', 'both_setsid_modes')
+def test_working_directories():
+    """The child process must start in the working directory in which
+    dumb-init was invoked, but dumb-init itself should not keep a
+    reference to that."""
+
+    # We need absolute path to dumb-init since we pass cwd=/tmp to get
+    # predictable output - so we can't rely on dumb-init being found
+    # in the "." directory.
+    proc = run((os.path.join(os.getcwd(), 'dumb-init'),
+                'sh', '-c', 'readlink /proc/$PPID/cwd && readlink /proc/$$/cwd'),
+               cwd="/tmp", stdout=PIPE, stderr=PIPE)
+
+    assert proc.returncode == 0
+    assert proc.stdout == b'/\n/tmp\n'