Drop ZEO tests with storages `DemoStorage`, `FileStorage` and...

Drop ZEO tests with storages `DemoStorage`, `FileStorage` and `HexFileStorage`; `FileStorage` is still tested in the variants with server side blobs and with shared blobs

CHANGES.rst

@@ -4,6 +4,18 @@ Changelog
 5.4.0 (unreleased)
 ------------------
 
+- Test ZEO only with the following storages
+  ``FileStorage`` with server side blobs,
+  ``FileStorage`` with shared blob directory,
+  ``MappingStorage`` (without blobs).
+
+  Those tests cover all storage features with impact on ZEO:
+  without blobs, with shared blobs and with server side blobs;
+  load, store, two phase commit, undo.
+  Therefore, passing tests for those storages provide high confidence that ZEO
+  works for other properly implemented storages as well.
+  See `#198 <https://github.com/zopefoundation/ZEO/issues/198>`_.
+
 - Lint the code with flake8
 
 - Add support for Python 3.10.

src/ZEO/tests/testZEO.py

@@ -1740,9 +1740,13 @@ def can_use_empty_string_for_local_host_on_client():
 
 slow_test_classes = [
     BlobAdaptedFileStorageTests, BlobWritableCacheTests,
-    MappingStorageTests, DemoStorageTests,
-    FileStorageTests,
-    FileStorageHexTests, FileStorageClientHexTests,
+    # keep to test a storage without blobs
+    # and with in memory store (may have different latency than
+    # ``FileStorage`` and therefore expose other race conditions)
+    MappingStorageTests,
+#   DemoStorageTests,
+#   FileStorageTests,
+#   FileStorageHexTests, FileStorageClientHexTests,
     ]
 if not forker.ZEO4_SERVER:
     slow_test_classes.append(FileStorageSSLTests)