Alternator's various write operations have different code paths for the
different write isolation modes. Because most of the test suite runs in
only a single write mode (currently - only_rmw_uses_lwt), we already
introduced a test file test/alternator/test_write_isolation.py for
checking the different write operations in *all* four write isolation
modes.
But we missed testing one write operation - BatchWriteItem. This
operation isn't very "interesting" because it doesn't support *any*
read-modify-option option (it doesn't support UpdateExpression,
ConditionExpression or ReturnValues), but even without those, the
pure write code still has different code paths with and without LWT,
and should be tested. So we add the missing test here - and it passes.
In issue #28439 we discovered a bug that can be seen in Alternator
Streams in the case of BatchWriteItem with multiple writes to the
same partition and always_use_lwt mode. The fact that the test added
here passes shows that the bug is NOT in BatchWriteItem itself, which
works correctly in this case - but only in the Alternator Streams layer.
Fixes#28171
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Before this patch, we had in test_condition_expression.py and
test_update_expression.py some rudimentary tests that the different
write isolation modes behave as expected. Basically, we wanted to test
that read-modify-write (RMW) operations are recognized and forbidden
in forbid_rmw mode, but work correctly in the three other modes.
We only check non-concurrent writes, so the actual write isolation is
NOT checked, just the correctness of non-concurrent writes.
However, since these tests were split across several files, and many
of the tests just ran other existing tests in different write isolation
modes, it was hard to see what exactly was being tested, and what was
missed. And indeed we missed checking some RMW operations, such as
requests with ReturnValues, requests with the older Expected or
AttributeUpdates (only the newer ConditionExpression and UpdateExpression
were tested), and ADD and DELETE operations in UpdateExpression.
So this patch replaces the existing partial tests with a new test file
test_write_isolation.py dedicated to testing all kinds of RMW operations
in one place, and how they don't work in forbid_rmw and do work in
the other modes. Writing all these tests in one place made it easier
to create a really exhaustive test of all the different operations and
optional parameters, and conversely - make sure that we don't test
*unnecessary* things such as different ConditionExpression expressions
(we already have 1800 lines of tests for ConditionExpression, and the
actual content of the condition is unrelated to write isolation modes).
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
