diff --git a/tests/test_app_filter.py b/tests/test_app_filter.py
new file mode 100644
index 0000000..6fcb16b
--- /dev/null
+++ b/tests/test_app_filter.py
@@ -0,0 +1,50 @@
+from __future__ import annotations
+
+from auditui.app import Auditui
+from auditui.search_utils import build_search_text, filter_items
+
+
+class StubLibrary:
+    def extract_title(self, item: dict) -> str:
+        return item.get("title", "")
+
+    def extract_authors(self, item: dict) -> str:
+        return item.get("authors", "")
+
+
+def test_get_search_text_is_cached() -> None:
+    class Dummy:
+        def __init__(self) -> None:
+            self._search_text_cache: dict[int, str] = {}
+            self.library_client = StubLibrary()
+
+    item = {"title": "Title", "authors": "Author"}
+    dummy = Dummy()
+    first = Auditui._get_search_text(dummy, item)
+    second = Auditui._get_search_text(dummy, item)
+    assert first == "title author"
+    assert first == second
+    assert len(dummy._search_text_cache) == 1
+
+
+def test_filter_items_uses_cache() -> None:
+    library = StubLibrary()
+    cache: dict[int, str] = {}
+    items = [
+        {"title": "Alpha", "authors": "Author One"},
+        {"title": "Beta", "authors": "Author Two"},
+    ]
+
+    def cached(item: dict) -> str:
+        cache_key = id(item)
+        if cache_key not in cache:
+            cache[cache_key] = build_search_text(item, library)
+        return cache[cache_key]
+
+    result = filter_items(items, "beta", cached)
+    assert result == [items[1]]
+
+
+def test_build_search_text_without_library() -> None:
+    item = {"title": "Title", "authors": [{"name": "A"}, {"name": "B"}]}
+    assert build_search_text(item, None) == "title a, b"