Add assertion to be contained by

[sunesimonsen]

I always implement this assertion as it is pretty useful:

expect(4, 'to be contained by', [1,2,3,4,5]);

[bruderstein]

'to be contained in' rather than by? "contained by" sounds odd.

[sunesimonsen]

@bruderstein I'm obviously not a native English speaker :-) So let's just use `to be contained in'.

[msiebuhr]

Yay! I've been lacking a to be a su(b|per)set of for quite a few tests recently.

[msiebuhr]

Here's my hacked together subset-check: Feel free to pifler as needed :)

expect.addAssertion('<any> to be a subset of <array>', function (expect, has, wantAtLeast) {
    if (!Array.isArray(has)) { has = [has]; }

    // See what's common between both sets
    var intersection = _.intersection(has, wantAtLeast);

    // If all input is in the common set, we're OK
    if (intersection.length !== has.length) {
        expect.fail({
            message: function (output) {
                return 'Expected', has, 'to be in', wantAtLeast;
            },
            diff: function (output, diff, inspect, equal) {
                return diff(has.sort(), intersection.sort());
            }
        });
    }
});

Generally, I've been missing some set theory in here; I'm currently writing a lot of API stubs where I have to check that returned data has one of some known values in certain properties.

Come to think of it, being able to do

expect(resp, 'to satisfy', {
    platform: expect.it('to be one of', ['ios', 'android', 'kindle']),
    ...
});

[papandreou]

@msiebuhr That looks very useful!

http://unexpected.js.org/unexpected-set/ already supports <Set> to satisfy <array-like> which roughly means that all items in the set have to be satisfied by an item in the array. That might be a good place to land something like this.

[msiebuhr]

You're welcome!

I'm not using sets (hello, Node 0.12.x) and I generally avoid using to satisfy, as its meaning can be quite ambiguous.

[papandreou]

As for the last snippet, this works today:

expect(resp, 'to satisfy', {
    platform: expect.it('to equal', 'ios').or('to equal', 'android').or('to equal', 'kindle')
});

[papandreou]

I'm not using sets (hello, Node 0.12.x)

The scope of unexpected-set includes exploring assertions with set semantics. It includes a Set polyfill, which is not applied globally, but which can be implicitly utilized via the with set semantics middle-of-the-rocket assertion.

and I generally avoid using to satisfy, as its meaning can be quite ambiguous.

Really? What sort of thing have you run into?

[msiebuhr]

Really? What sort of thing have you run into?

In unexpected-moment, to satisfy is aliased to moment.isSame() (source), while unexpected-set quite obviously isn't that simple (~150 SLOC).

In general, I don't trust that I other people on the project can figure out the semantics of expect(result, 'to satisfy', some-value-or-other) without having to look in the documentation. For the general cases with objects and unexpected-sets list-of-assertions, it's usually obvious, but the exact semantics requires quite a few roundtrips to the documentation.

Having to be a subset of and to be a superset of would make it simple, explicit and straightforward.

platform: expect.it('to equal', 'ios').or('to equal', 'android').or('to equal', 'kindle')

A bit more stutter, but I guess that can do for now.

Also - it does seem one can build quite complex assertions with chains of .and and .or, but I can't quite find out how to make grouping explicit. Anything I missed?

[sunesimonsen]

The only documentation of expect.it is in to satisfy, we should probably try to explain the precedence a little bit better - it is only the indentation that gives a clue. The same indentation is also used when outputting expect.it in an error message.

platform: expect.it('to equal', 'ios').or('to equal', 'android').or('to equal', 'kindle')

This is horrible - you should just make a custom assertion if it is not provided by a plugin.

I don't want set operations in core, I think it belongs in unexpected-set. But strictly speaking it is also wrong to use arrays as sets, maybe another terminology could be used:

expect(['a', 'b', 'c'], 'to be contained in', ['a', 'b', 'c', 'b', 'd'])
expect(['a', 'b', 'c'], 'to contain', 'a', 'b')

The last assertion already exists but it is unfortunately varargs :-(