Add ``assert_equal`` to TableCollection and TreeSequence

[jeromekelleher]

The '.equalsmethod is very useful, but it doesn't tell us where the problem is when tables are not equal. We should add methodsassert_equal`` which would initially look like

def assert_equal(self, other, ignore_provenance=...) # same signature as equals
    assert self.sequence_length == other.sequence_length
    assert self.nodes == other.nodes
    # etc

This would at least tell us which table the mismatch occurs in. We can imagine providing a more detailed picture of how tables differ at some point, but this could be added later as a refinement. This form assert_equal should integrate nicely with pytest, and clean up our testing code some more.

Seems like a straightforward win?

[hyanwong]

Definitely. The other way would be for the equality testing code to break at different places. E.g. if it were in python, you could do:

def equals(self, other):
    if self.table1 != other.table1:
         return False
    if self.table2 != other.table2:
         return False
    ...
    return True

But AFAIK the comparison is in C, so I guess that's not so easy, and a separate assert_equals function (for Python only?) is a much easier win.

[jeromekelleher]

Yes, this is Python only.

[petrelharp]

Here's a draft of that: https://github.com/tskit-dev/pyslim/blob/fe1f7fab11b5a529eacd6f404fcf32ba00c181a5/tests/__init__.py#L342

[jeromekelleher]

Reopening this, as we want it to be part of the public API.