All other multiparameter assignment tests are in the same file, so it
makes sense to have all of them here.

does not have TIME data type.

Fixes #6825, adds tests covering cases and error possibilities, also changes SQLite3 driver to correctly generate a time column instead of datetime

This reverts commit fa6d921e.

Reason: Not a fan of such massive changes. We usually close such changes
if made to Rails master as a pull request. Following the same principle
here and reverting.

[ci skip]

For future reference, this is the regex I used: ^\s*#\s*\n(?!\s*#). Replace
with the first match, and voilà! Note that the regex matches a little bit too
much, so you probably want to `git add -i .` and go through every single diff
to check if it actually should be changed.

This reverts commit 7381596e.

We also need to time zone convert time zone aware attributes when
accessed via read_attribute, not only when via direct access.

This makes me happy!

Implement a mini state machine for serialized attributes. This means we
do not have to deserialize the values upon initialization, which means
that if we never actually access the attribute, we never have to
deserialize it.

"Returns true if the specified attribute has been set by the user or by
a database load and is neither nil nor empty?"

Fixes #1613

There is no meaningful performance penalty in defining attribute
methods, since it only happens once.

There is also no reason *not* to define them, since they get thrown in
an included module, so they will not 'overwrite' anything. In fact, this
is desirable, since it allows us to call super.

This shouldn't ever happen unless people are doing something
particularly weird, but adding a deprecation in case there are bugs not
caught by our tests.

Check respond_to_without_attributes? in method_missing. If there is any
method that responds (even private), let super handle it and raise
NoMethodError if necessary.

This fixes a situation I encountered where a subclass would cache the
name of a generated attribute method in @_defined_class_methods. Then,
when the superclass has it's attribute methods undefined, the subclass
would always have to dispatch through method_missing, because the
presence of the attribute in @_defined_class_methods would mean that it
is never generated again, even if undefine_attribute_methods is called
on the subclass.

There various other confusing edge cases like this. STI classes share
columns, so let's just keep all the attribute method generation state
isolated to the base class.

This reverts commit 87152f26, reversing
changes made to 0d3615f0.

Refactor Active Record test connection setup. Please see the RUNNING_UNIT_TESTS file for details, but essentially you can now configure things in test/config.yml. You can also run tests directly via the command line, e.g. ruby path/to/test.rb (no rake needed, uses default db connection from test/config.yml). This will help us fix the CI by enabling us to isolate the different Rails versions to different databases.