diff --git a/tests/test_file_crypto_extras.py b/tests/test_file_crypto_extras.py
new file mode 100644
index 0000000..c4cd5df
--- /dev/null
+++ b/tests/test_file_crypto_extras.py
@@ -0,0 +1,125 @@
+import os
+import tempfile
+
+import pytest
+
+from ChatApp import file_crypto
+
+
+class DummyEncryptor:
+    def __init__(self):
+        self.tag = b't' * 16
+
+    def update(self, data):
+        raise RuntimeError('boom')
+
+    def finalize(self):
+        pass
+
+
+class DummyCipherEnc:
+    def __init__(self, *a, **k):
+        pass
+
+    def encryptor(self):
+        return DummyEncryptor()
+
+
+class DummyDecryptor:
+    def update(self, data):
+        return data
+
+    def finalize_with_tag(self, tag):
+        raise RuntimeError('bad tag')
+
+
+class DummyCipherDec:
+    def __init__(self, *a, **k):
+        pass
+
+    def decryptor(self):
+        return DummyDecryptor()
+
+
+def test_encrypt_file_cleanup_on_error(monkeypatch):
+    with tempfile.TemporaryDirectory() as tmp:
+        plain = os.path.join(tmp, 'plain')
+        enc = os.path.join(tmp, 'enc')
+        with open(plain, 'wb') as fh:
+            fh.write(b'data')
+
+        monkeypatch.setattr(file_crypto, 'Cipher', DummyCipherEnc)
+        with pytest.raises(RuntimeError):
+            file_crypto.encrypt_file(plain, enc, 'pw')
+        assert not os.path.exists(enc)
+
+
+def test_decrypt_file_too_small():
+    with tempfile.TemporaryDirectory() as tmp:
+        infile = os.path.join(tmp, 'small')
+        outfile = os.path.join(tmp, 'out')
+        with open(infile, 'wb') as fh:
+            fh.write(b'123')
+        with pytest.raises(ValueError):
+            file_crypto.decrypt_file(infile, outfile, 'pw')
+
+
+def test_decrypt_file_cleanup_on_error(monkeypatch):
+    with tempfile.TemporaryDirectory() as tmp:
+        plain = os.path.join(tmp, 'plain')
+        enc = os.path.join(tmp, 'enc')
+        dec = os.path.join(tmp, 'dec')
+        with open(plain, 'wb') as fh:
+            fh.write(b'secret data')
+        file_crypto.encrypt_file(plain, enc, 'pw')
+
+        monkeypatch.setattr(file_crypto, 'Cipher', DummyCipherDec)
+        with pytest.raises(RuntimeError):
+            file_crypto.decrypt_file(enc, dec, 'pw')
+        assert not os.path.exists(dec)
+
+class StopEarlyFile:
+    def __init__(self, fh):
+        self._fh = fh
+        self.calls = 0
+
+    def __enter__(self):
+        self._fh.__enter__()
+        return self
+
+    def __exit__(self, exc_type, exc, tb):
+        return self._fh.__exit__(exc_type, exc, tb)
+
+    def read(self, size=-1):
+        self.calls += 1
+        data = self._fh.read(size)
+        if self.calls > 3:
+            return b''
+        return data
+
+    def __getattr__(self, item):
+        return getattr(self._fh, item)
+
+
+def test_decrypt_file_breaks_on_short_read(monkeypatch):
+    with tempfile.TemporaryDirectory() as tmp:
+        plain = os.path.join(tmp, 'plain')
+        enc = os.path.join(tmp, 'enc')
+        dec = os.path.join(tmp, 'dec')
+        with open(plain, 'wb') as fh:
+            fh.write(b'some data to encrypt')
+        file_crypto.encrypt_file(plain, enc, 'pw')
+
+        real_open = open
+
+        def bad_open(path, mode='rb', *args, **kwargs):
+            fh = real_open(path, mode, *args, **kwargs)
+            if path == enc and 'rb' in mode:
+                return StopEarlyFile(fh)
+            return fh
+
+        import builtins
+        monkeypatch.setattr(builtins, 'open', bad_open)
+        with pytest.raises(Exception):
+            file_crypto.decrypt_file(enc, dec, 'pw', chunk_size=1)
+        assert not os.path.exists(dec)
diff --git a/tests/test_settings_demo.py b/tests/test_settings_demo.py
new file mode 100644
index 0000000..7b1ea4c
--- /dev/null
+++ b/tests/test_settings_demo.py
@@ -0,0 +1,26 @@
+import importlib
+import sys
+import types
+
+import pytest
+
+
+def test_settings_demo_import(monkeypatch):
+    class DummyCelery:
+        def __init__(self, *a, **k):
+            pass
+
+        def config_from_object(self, *a, **k):
+            pass
+
+        def autodiscover_tasks(self):
+            pass
+
+    monkeypatch.setitem(sys.modules, 'celery', types.SimpleNamespace(Celery=DummyCelery))
+    module = importlib.import_module('WebSocketChatApp.settings_demo')
+
+    assert module.DEBUG is True
+    assert module.USE_DEV_AUTH is True
+    assert module.CELERY_BROKER_URL is None
+    assert module.ALLOWED_HOSTS == ['*']
+    assert module.WEBSOCKET_ALLOWED_ORIGINS == ['*']