Implement Transaction#mutated?

[no-reply]

#mutated? must return true when the transaction would change the
repository if executed against it's state at transaction start time.
We allow implementations to return true in other cases, as well; there
is no guarantee that a false result will be returned in any specific
circumstances (or ever).

For the base transaction, we simply check whether @changes is
empty. This can give false positives, but avoids a worst-case linear
check.

For subclasses with no custom implementation, we raise a
NotImplementedError.

For the SerializableTransaction included in the default
Repository::Implementation, we use #equal? on the Hamster::Hash
instances. This will always give a correct response for the actual
implementation, moreover, it is guaranteed not to give false negatives
even if a user messes with the snapshot using #send.

Closes #308.

[coveralls]

Coverage decreased (-0.01%) to 90.971% when pulling 729d251 on feature/tx-mutated into fc06d1f on develop.

[no-reply]

Do we have a way to silence dependency-ci on wirble and convince it that rdf-isomorphic is maintained

[no-reply]

Note the caveats about false positives.

I considered the possibility of using true and false return values only when status is guaranteed. A "truthy" (but not == true) value would be given where as false positive is possible (as in the base class).

This seems viable, but I opted for the simpler approach as a starting place.

[coveralls]

Coverage decreased (-0.01%) to 90.971% when pulling 7a6ae88 on feature/tx-mutated into fc06d1f on develop.

[gkellogg]

I think you got it right. Don't know about silencing depend nicest, but it's intended to make our lives easier, not harder. See what you can figure out.

[no-reply]

What do you think about just dropping the wirble dependency? Do you use that in development?

I let libraries.io know through their form that rdf-isomorphic is still maintained. I'm kind of hoping they'll explain where they got the idea it wasn't.

[gkellogg]

Dropping warble should be fine, it seems to be more of a pain than it's worth.

WRT rdf-isomorphic, probably because no recent releases, although there was a commit in July.

[coveralls]

Changes Unknown when pulling fe1a3f8 on feature/tx-mutated into * on develop*.

[coveralls]

Changes Unknown when pulling d94cd14 on feature/tx-mutated into * on develop*.