test: add error-path tests for all bug fixes

- test_doveauth: invalid localpart chars rejected, concurrent same-account creation
- test_expire: --mdir filtering uses msg.path correctly
- test_metadata: TURN exception returns N\n, success returns credentials
- test_turnserver: socket timeout, connection refused, happy path
- test_dns: get_dkim_entry returns (None, None) on CalledProcessError
- test_rshell: dovecot_recalc_quota handles empty/malformed output

cmdeploy/src/cmdeploy/tests/test_dns.py

@@ -60,6 +60,29 @@ def mockdns(request, mockdns_base, mockdns_expected):
     return mockdns_base
 
 
+class TestGetDkimEntry:
+    def test_dkim_entry_returns_tuple_on_success(self, mockdns):
+        entry, web_entry = remote.rdns.get_dkim_entry(
+            "some.domain", "", dkim_selector="opendkim"
+        )
+        # May return None,None if openssl not available, but should never crash
+        if entry is not None:
+            assert "opendkim._domainkey.some.domain" in entry
+            assert "opendkim._domainkey.some.domain" in web_entry
+
+    def test_dkim_entry_returns_none_tuple_on_error(self, monkeypatch):
+        """CalledProcessError must return (None, None), not bare None."""
+        from subprocess import CalledProcessError
+
+        def failing_shell(command, fail_ok=False, print=print):
+            raise CalledProcessError(1, command)
+
+        monkeypatch.setattr(remote.rdns, "shell", failing_shell)
+        result = remote.rdns.get_dkim_entry("some.domain", "", dkim_selector="opendkim")
+        assert result == (None, None)
+        assert result[0] is None and result[1] is None
+
+
 class TestPerformInitialChecks:
     def test_perform_initial_checks_ok1(self, mockdns, mockdns_expected):
         remote_data = remote.rdns.perform_initial_checks("some.domain")

cmdeploy/src/cmdeploy/tests/test_rshell.py

@@ -0,0 +1,68 @@
+from unittest.mock import patch
+
+from cmdeploy.remote.rshell import dovecot_recalc_quota
+
+
+def test_dovecot_recalc_quota_normal_output():
+    """Normal doveadm output returns parsed dict."""
+    normal_output = (
+        "Quota name Type    Value  Limit  %\n"
+        "User quota STORAGE     5 102400  0\n"
+        "User quota MESSAGE     2      -  0\n"
+    )
+
+    with patch("cmdeploy.remote.rshell.shell", return_value=normal_output):
+        result = dovecot_recalc_quota("user@example.org")
+
+    # shell is called twice (recalc + get), patch returns same for both
+    assert result == {"value": 5, "limit": 102400, "percent": 0}
+
+
+def test_dovecot_recalc_quota_empty_output():
+    """Empty doveadm output (trailing newline) must not IndexError."""
+    call_count = [0]
+
+    def mock_shell(cmd):
+        call_count[0] += 1
+        if "recalc" in cmd:
+            return ""
+        # quota get returns only empty lines
+        return "\n\n"
+
+    with patch("cmdeploy.remote.rshell.shell", side_effect=mock_shell):
+        result = dovecot_recalc_quota("user@example.org")
+
+    assert result is None
+
+
+def test_dovecot_recalc_quota_malformed_output():
+    """Malformed output with too few columns must not crash."""
+    call_count = [0]
+
+    def mock_shell(cmd):
+        call_count[0] += 1
+        if "recalc" in cmd:
+            return ""
+        # partial line, fewer than 6 parts
+        return "Quota name\nUser quota STORAGE\n"
+
+    with patch("cmdeploy.remote.rshell.shell", side_effect=mock_shell):
+        result = dovecot_recalc_quota("user@example.org")
+
+    assert result is None
+
+
+def test_dovecot_recalc_quota_header_only():
+    """Only header line, no data rows."""
+    call_count = [0]
+
+    def mock_shell(cmd):
+        call_count[0] += 1
+        if "recalc" in cmd:
+            return ""
+        return "Quota name Type    Value  Limit  %\n"
+
+    with patch("cmdeploy.remote.rshell.shell", side_effect=mock_shell):
+        result = dovecot_recalc_quota("user@example.org")
+
+    assert result is None