diff --git a/dnstapir/key_resolver.py b/dnstapir/key_resolver.py
index b70dac7..ff8ed7a 100644
--- a/dnstapir/key_resolver.py
+++ b/dnstapir/key_resolver.py
@@ -32,7 +32,6 @@ def key_resolver_from_client_database(client_database: str, key_cache: KeyCache
 
 
 class KeyResolver:
-
     def __init__(self):
         self.logger = logging.getLogger(__name__).getChild(self.__class__.__name__)
 
diff --git a/tests/test_key_resolver.py b/tests/test_key_resolver.py
index 6742a51..144c8df 100644
--- a/tests/test_key_resolver.py
+++ b/tests/test_key_resolver.py
@@ -1,9 +1,32 @@
+from pathlib import Path
+from tempfile import TemporaryDirectory
+
 import pytest
 from cryptography.hazmat.primitives import serialization
 from cryptography.hazmat.primitives.asymmetric import ed25519
 from pytest_httpx import HTTPXMock
 
-from dnstapir.key_resolver import UrlKeyResolver
+from dnstapir.key_resolver import FileKeyResolver, UrlKeyResolver
+
+
+def test_file_key_resolver(httpx_mock: HTTPXMock):
+    key_id = "xyzzy"
+    public_key = ed25519.Ed25519PrivateKey.generate().public_key()
+    public_key_pem = public_key.public_bytes(
+        encoding=serialization.Encoding.PEM, format=serialization.PublicFormat.SubjectPublicKeyInfo
+    )
+
+    with TemporaryDirectory(prefix="dnstapir") as directory:
+        pem_filename = Path(directory) / f"{key_id}.pem"
+        with open(pem_filename, "wb") as fp:
+            fp.write(public_key_pem)
+
+        resolver = FileKeyResolver(client_database_directory=directory)
+        res = resolver.resolve_public_key(key_id)
+        assert res == public_key
+
+        with pytest.raises(KeyError):
+            _ = resolver.resolve_public_key("unknown")
 
 
 def test_url_key_resolver(httpx_mock: HTTPXMock):
@@ -21,7 +44,7 @@ def test_url_key_resolver(httpx_mock: HTTPXMock):
     assert res == public_key
 
     with pytest.raises(KeyError):
-        res = resolver.resolve_public_key("unknown")
+        _ = resolver.resolve_public_key("unknown")
 
 
 def test_url_key_resolver_pattern(httpx_mock: HTTPXMock):
@@ -39,7 +62,7 @@ def test_url_key_resolver_pattern(httpx_mock: HTTPXMock):
     assert res == public_key
 
     with pytest.raises(KeyError):
-        res = resolver.resolve_public_key("unknown")
+        _ = resolver.resolve_public_key("unknown")
 
 
 def test_url_key_resolver_contextlib(httpx_mock: HTTPXMock):
@@ -50,7 +73,11 @@ def test_url_key_resolver_contextlib(httpx_mock: HTTPXMock):
     )
 
     httpx_mock.add_response(url=f"https://keys/{key_id}.pem", content=public_key_pem)
+    httpx_mock.add_response(url="https://keys/unknown.pem", status_code=404)
 
     with UrlKeyResolver(client_database_base_url="https://keys") as resolver:
         res = resolver.resolve_public_key(key_id)
         assert res == public_key
+
+    with pytest.raises(KeyError):
+        _ = resolver.resolve_public_key("unknown")