Use runtimeType in expect/throwsA

[DartBot]

This issue was originally filed by @sethladd

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This doc is what the docs recommends:

expect(() => store.keys(), throwsA(new isInstanceOf<StateError>()));

However, we now have .runtimeType. Can we instead make the matcher more simple?

This works:

test(obj, Type type) {
  return (obj.runtimeType == type);
}

void main() {
  print(test(new StateError('foo'), StateError));
}

I'd love to see:

expect(() => store.keys(), throwsA(StateError));

Thoughts?

[DartBot]

This comment was originally written by @sethladd

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Drat. Title should be something like: "Add a match to match against type"

[lrhn]

Notice that this only tests for type equality, not subtype relation.
If the StateError thrown is actually an internal subtype of StateError, the test will fail, event though it is a StateError.

It really needs to be a subtype test in order to maintain the substitution principle.
A workaround is to always override runtimeType on internal classes, but I don't think it's feasible in practice.

In the longer run, we might want to allow type objects as the right-hand operand of the "is" operator.

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Added Area-Pkg, Package-Unittest, Triaged labels.
Changed the title to: "Use runtimeType in expect/throwsA".

[DartBot]

This comment was originally written by @butlermatt

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I'm curious why this error does not have a pre-set matcher similar to 'throwsArgumentError' or 'throwsRangeError' etc. I realize not all errors are represented here but I would think stateError to be used enough to warrant its inclusion.

[munificent]

It should be. I think it's just that the pre-set matchers were created before the Great Exception Type Cleanup of 2013. File a separate bug for this?

[DartBot]

This comment was originally written by @sethladd

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One step ahead: http://code.google.com/p/dart/issues/detail?id=8137 :)

[DartBot]

This comment was originally written by @sethladd

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Lasse, you're right. I poorly worded the title. Instead, a better title should be: "Add a matcher that tests an object's type and that works in dart2js"

Thanks for the clarification!

[gramster]

I'm not sure now whether you still want this, Seth. It seems without subtype support it isn't very useful.

[scheglov]

Yes.
Can we have subtype support in language please? :-)

[gramster]

Issue #10407 has been merged into this issue.

[DartBot]

This comment was originally written by @seaneagan

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This should be marked as blocked on issue #10406.

[sethladd]

Added AssumedStale label.