Write a test for safe_unlink (#6311)

write a test for safe_unlink

src/borg/testsuite/helpers.py

@@ -1,3 +1,4 @@
+import errno
 import hashlib
 import os
 import shutil
@@ -30,6 +31,7 @@
 from ..helpers import dash_open
 from ..helpers import iter_separated
 from ..helpers import eval_escapes
+from ..helpers import safe_unlink
 
 from . import BaseTestCase, FakeInputs
 
@@ -1133,3 +1135,32 @@ def test_iter_separated():
 def test_eval_escapes():
     assert eval_escapes('\\n\\0\\x23') == '\n\0#'
     assert eval_escapes('äç\\n') == 'äç\n'
+
+
+def test_safe_unlink_is_safe(tmpdir):
+    contents = b"Hello, world\n"
+    victim = tmpdir / 'victim'
+    victim.write_binary(contents)
+    hard_link = tmpdir / 'hardlink'
+    hard_link.mklinkto(victim)
+
+    safe_unlink(hard_link)
+
+    assert victim.read_binary() == contents
+
+
+def test_safe_unlink_is_safe_ENOSPC(tmpdir, monkeypatch):
+    contents = b"Hello, world\n"
+    victim = tmpdir / 'victim'
+    victim.write_binary(contents)
+    hard_link = tmpdir / 'hardlink'
+    hard_link.mklinkto(victim)
+
+    def os_unlink(_):
+        raise OSError(errno.ENOSPC, "Pretend that we ran out of space")
+    monkeypatch.setattr(os, "unlink", os_unlink)
+
+    with pytest.raises(OSError):
+        safe_unlink(hard_link)
+
+    assert victim.read_binary() == contents