pkg/matcher: isEmpty should fail for null or non-collections.

[DartBot]

Originally opened as dart-lang/sdk#21562

This issue was originally filed by [email protected]

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As there is no isNotEmpty matcher, you are forced to use isNot(isEmpty). However, expect(null, isNot(isEmpty)) passes because isEmpty returns false for non-collections or null. So, likewise, any other non-collection object would also wrongly pass such an expect call.

My suggested solution would be for isEmpty to throw an exception for "wrong" types.

Alternatively, an isNotEmpty matcher could be added.

Thanks,
 Andreas

[DartBot]

<img src="https://avatars.githubusercontent.com/u/4865287?v=3" align="left" width="48" height="48"hspace="10"> Comment by lrhn

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Removed Type-Defect label.
Added Type-Enhancement, Area-Pkg, Pkg-Unittest, Triaged labels.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/17034?v=3" align="left" width="48" height="48"hspace="10"> Comment by kevmoo

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Added Community-Idea, Community-StarterBug labels.

[DartBot]

This comment was originally written by [email protected]

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I'd call this a defect because except(myCollection, isNot(isEmpty)) not failing for null references can hide nasty bugs.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/17034?v=3" align="left" width="48" height="48"hspace="10"> Comment by kevmoo

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Fair.

We can wrap up a new isNotEmpty up as the new feature – depending on how this lands.

This would be an easy fix in pkg/matcher. Patches welcome.

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Removed Type-Enhancement label.
Added Type-Defect label.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/17034?v=3" align="left" width="48" height="48"hspace="10"> Comment by kevmoo

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Removed Pkg-Unittest label.
Added Pkg-matcher label.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/17034?v=3" align="left" width="48" height="48"hspace="10"> Comment by kevmoo

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dart-archive/matcher@755ee44

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Added Fixed label.