feat(rules): load a shared tagging-rule store

The rules that tag incoming mail live in a notmuch post-new hook as
hand-written shell. This is the first piece of moving them into a JSON
store that both this tool and qtmaildir read.

A rule carries no scope: the hook supplies tag:new, a dry run supplies
nothing. Unknown fields are kept per rule so the format belongs to
neither tool.

1 files changed, 94 insertions, 0 deletions

diff --git a/test_mailrules.py b/test_mailrules.py
new file mode 100755
index 0000000..dd491e9
--- /dev/null
+++ b/test_mailrules.py
@@ -0,0 +1,94 @@
+#!/usr/bin/env python3
+#
+# Copyright (C) 2026 Danilo M. <danix@danix.xyz>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+"""Self-checks for mailrules.py, the shared tagging-rule store.
+
+The risk in this file is the format, not the notmuch calls: a rule that
+silently loses a field on save, or one that sorts into the wrong stage,
+mis-tags real mail on the next sync and does it quietly.
+
+Run: ./test_mailrules.py
+"""
+
+import json
+import tempfile
+from pathlib import Path
+
+import mailrules
+
+
+def write_rules(tmp, payload):
+    path = Path(tmp) / "rules.json"
+    path.write_text(json.dumps(payload))
+    return path
+
+
+def test_loads_a_rule():
+    with tempfile.TemporaryDirectory() as tmp:
+        path = write_rules(tmp, {
+            "version": 1,
+            "rules": [
+                {
+                    "id": "notify-forge",
+                    "stage": 50,
+                    "enabled": True,
+                    "add": ["notify/forge"],
+                    "remove": [],
+                    "query": "from:notifications@example.com",
+                    "note": "All repositories, not one project.",
+                }
+            ],
+        })
+        store = mailrules.load(path)
+        assert store.warnings == [], store.warnings
+        assert len(store.rules) == 1
+        rule = store.rules[0]
+        assert rule.id == "notify-forge"
+        assert rule.stage == 50
+        assert rule.enabled is True
+        assert rule.add == ["notify/forge"]
+        assert rule.remove == []
+        assert rule.query == "from:notifications@example.com"
+        assert rule.note == "All repositories, not one project."
+
+
+def test_defaults_are_applied():
+    """stage, enabled, remove and note are all optional in the file."""
+    with tempfile.TemporaryDirectory() as tmp:
+        path = write_rules(tmp, {
+            "version": 1,
+            "rules": [{"id": "minimal", "add": ["x"],
+                       "query": "from:someone@example.com"}],
+        })
+        store = mailrules.load(path)
+        assert store.warnings == [], store.warnings
+        rule = store.rules[0]
+        assert rule.stage == 50
+        assert rule.enabled is True
+        assert rule.remove == []
+        assert rule.note == ""
+
+
+def run_all():
+    for name, fn in sorted(globals().items()):
+        if name.startswith("test_") and callable(fn):
+            fn()
+            print(f"ok  {name}")
+
+
+if __name__ == "__main__":
+    run_all()
+    print("\nall passed")