test: cover build_filter (participant should-clause, date ranges, combination)

tests/test_server.py

@@ -8,6 +8,7 @@ from server import (
     normalize_email_address,
     payload_matches_participant,
     format_search_result,
+    build_filter,
 )
 
 
@@ -108,3 +109,55 @@ class TestFormatSearchResult:
         assert result["receiver"] is None
         assert result["subject"] is None
         assert result["attachments"] == []
+
+
+class TestBuildFilter:
+    def test_no_filters_returns_none(self):
+        assert build_filter(None, None, None) is None
+
+    def test_empty_strings_return_none(self):
+        assert build_filter("", "", "") is None
+
+    def test_participant_filter_is_should_clause_on_sender_and_receiver(self):
+        f = build_filter("alice@example.com", None, None)
+        assert f is not None
+        # The date conditions list must be absent and only the participant filter present
+        assert len(f.must) == 1
+        participant = f.must[0]
+        keys = [c.key for c in participant.should]
+        assert keys == ["sender", "receiver"]
+        assert all(c.match.value == "alice@example.com" for c in participant.should)
+
+    def test_participant_normalized_before_match(self):
+        f = build_filter("Alice <Alice@Example.COM>", None, None)
+        should = f.must[0].should
+        assert all(c.match.value == "alice@example.com" for c in should)
+
+    def test_date_range_only(self):
+        f = build_filter(None, "2026-01-01", "2026-06-30")
+        assert len(f.must) == 1
+        cond = f.must[0]
+        assert cond.key == "date"
+        assert cond.range.gte is not None
+        assert cond.range.lte is not None
+
+    def test_start_date_only(self):
+        f = build_filter(None, "2026-03-15", None)
+        cond = f.must[0]
+        assert cond.range.gte is not None
+        assert cond.range.lte is None
+
+    def test_end_date_only(self):
+        f = build_filter(None, None, "2026-03-15")
+        cond = f.must[0]
+        assert cond.range.gte is None
+        assert cond.range.lte is not None
+
+    def test_combined_participant_and_date(self):
+        f = build_filter("bob@example.org", "2026-01-01", "2026-12-31")
+        assert len(f.must) == 2
+        # One is the participant should-filter, the other the date range
+        kinds = sorted(
+            "participant" if getattr(c, "should", None) else "date" for c in f.must
+        )
+        assert kinds == ["date", "participant"]