Previously we set up migrations directly as structs which doesn't match
how users will create them. For the new test framework, we'll instead
write TOML for migrations. This brings the tests closer to how an end
user will interact with Reshape and also lets us write tests to match
the examples in the documentation.
This reduces the amount of boilerplate required to run a test and also
has the added benefit of extending tests as we can now easily test both the
completion and abort paths. So far two tests have been ported over,
create_table and add_column, with the rest to follow.
The framework also improves the output of tests, adding sections clearly
indicating in which part of the migration process a test failed.
With the old fields in the `State` broken out we can now make `State` a
proper enum, replacing the nested `Status`. The naming with both `State`
and `Status` was a bit confusing.
Before, the entire state was stored as a JSON encoded blob including all
completed migrations. This commits moves the migrations into a dedicated
table, which prevents the encoded from growing indefinitely. The size of
the state probably wouldn't have become a problem but it feels weird for
a schema migration tool to not use a proper schema.
Next, the version stored in the state struct will be moved to a separate
key in the `reshape.data` table and `State` will become an enum with the
same structure as `Status`. The naming right now is a bit confusing.
Until now, using alter_column would cause indices to be lost as they
weren't copied to the temporary column. This fixes that for indices that
consist of one or more actual columns. It won't work for indices on
expressions.
The builder will help simplify the tests and avoid boilerplate updates
when need fields are added to the create_table migration. We might want
to add builders all migrations later.
This checks for dangling temporary columns, triggers and function which
were used by migrations but should be removed once the migration has
been completed or aborted.
