Add read-only tests.

Signed-off-by: Andrea Odetti <[email protected]>

tests/test_query_only.py

@@ -0,0 +1,64 @@
+import contextlib
+import os
+import shutil
+import sqlite3
+import stat
+import tempfile
+
+import pytest
+
+import diskcache as dc
+from diskcache.core import DBNAME, ReadOnlyError
+
+
+@pytest.fixture
+def cache_directory():
+    with contextlib.nullcontext(
+        tempfile.mkdtemp(prefix='diskcache-')
+    ) as directory:
+        yield directory
+        shutil.rmtree(directory, ignore_errors=True)
+
+
+def test_cannot_create(cache_directory):
+    with pytest.raises(sqlite3.OperationalError):
+        dc.Cache(directory=cache_directory, sqlite_query_only=True)
+
+
+def test_can_read_only(cache_directory):
+    key = 'some'
+    obj1 = [5, 6, 7]
+
+    # create the cache, must be in read write mode
+    rw = dc.Cache(directory=cache_directory)
+    rw[key] = obj1
+    rw = None
+
+    # make the file RO
+    os.chmod(os.path.join(cache_directory, DBNAME), stat.S_IREAD)
+
+    # with sqlite_query_only=True we can read the DB
+    ro = dc.Cache(directory=cache_directory, sqlite_query_only=True)
+    obj2 = ro[key]
+    ro = None
+
+    assert obj2 == obj1
+
+    # default cache cannot read a ro file
+    with pytest.raises(sqlite3.OperationalError):
+        dc.Cache(directory=cache_directory)
+
+
+def test_cannot_update(cache_directory):
+    # create the cache, must be in read write mode
+    rw = dc.Cache(directory=cache_directory)
+    rw['key'] = 'old'
+    rw = None
+
+    # re-open ro: cannot update
+    ro = dc.Cache(directory=cache_directory, sqlite_query_only=True)
+    with pytest.raises(ReadOnlyError):
+        ro['key'] = 'new'
+
+    with pytest.raises(ReadOnlyError):
+        ro.clear()