It seems that adding a restriction to allow_value to raise
CouldNotClearAttribute if nil cannot be set on the attribute in question
broke a lot of people's tests. Really the only reason we added this was
for validate_presence_of -- it rescued CouldNotClearAttribute and
re-raised it as CouldNotSetPasswordError, but only for passwords and
only if has_secure_password was being used. So, I've figured out another
way of performing this check inside of validate_presence_of only to
prevent tests that have nothing to do with from breaking unnecessarily.
If you have a model that declares `has_secure_password` and you also
have a presence validation on the password, and you write a test against
this validation using an instance of your model where the password is
already set, then your test will fail. This is because
has_secure_password (at least on Rails 4) defines #password= such that
if it is given nil, then the password will not be overwritten with nil.
This interferes with how our validate_presence_of matcher works.
Unfortunately there is not a great way to get around this (using
\#write_attribute won't work, either). So in this case we raise a
helpful error message that instructs the user to use an empty record
against `validates_presence_of`.
Currently, using `ensure_inclusion_of` against a boolean column doesn't
work. We can assert that the column allows boolean values, but what
about values that should be rejected? Well, it depends on what you give
to `ensure_inclusion_of`. Here's how it works now:
* `ensure_inclusion_of(:attr).in_array([true])` asserts that false is
rejected
* `ensure_inclusion_of(:attr).in_array([false])` asserts that true is
rejected
* `ensure_inclusion_of(:attr).in_array([true, false])` does not assert
that anything is rejected, instead informing the developer how
this sort of expectation is not fully testable (anything other than
true, false, or nil will be converted to false).
* `ensure_inclusion_of(:attr).in_array([nil])`, when the column is
nullable, does not assert that anything is rejected, either, also
printing a warning
* `ensure_inclusion_of(:attr).in_array([nil])`, when the column is
non-nullable, raises an error because this expectation is not testable
in any way, as setting a boolean column to nil this way will get
converted to false.
