And constraint on Has.Member throws

[ChrisFewtrell]

An example

var donkey = new object();
var mule = new object();
Assert.That(new[] { donkey }, Has.Member(donkey).And.No.Member(mule));

Fails with this exception in 3.8.1

System.ArgumentException : The actual value must be an IEnumerable
Parameter name: actual
   at NUnit.Framework.Constraints.SomeItemsConstraint.ApplyTo[TActual](TActual actual) in D:\git\nunit\src\NUnitFramework\framework\Constraints\SomeItemsConstraint.cs:line 64
   at NUnit.Framework.Constraints.NotConstraint.ApplyTo[TActual](TActual actual) in D:\git\nunit\src\NUnitFramework\framework\Constraints\NotConstraint.cs:line 48
   at NUnit.Framework.Constraints.AndConstraint.ApplyTo[TActual](TActual actual) in D:\git\nunit\src\NUnitFramework\framework\Constraints\AndConstraint.cs:line 64
   at NUnit.Framework.Constraints.SomeItemsConstraint.ApplyTo[TActual](TActual actual) in D:\git\nunit\src\NUnitFramework\framework\Constraints\SomeItemsConstraint.cs:line 65
   at NUnit.Framework.Assert.That[TActual](TActual actual, IResolveConstraint expression, String message, Object[] args) in D:\git\nunit\src\NUnitFramework\framework\Assert.That.cs:line 245
   at NUnit.Framework.Assert.That[TActual](TActual actual, IResolveConstraint expression) in D:\git\nunit\src\NUnitFramework\framework\Assert.That.cs:line 228
   at Granta.Services.FunctionalData.Tests.ParameterValueExtraction.ParameterSingleValuesExtractorDatabaseTests.MethodUsingObjectsFailsInDifferentManner() in D:\git\servicelayer\FunctionalDataTests\ParameterValueExtraction\ParameterSingleValuesExtractorDatabaseTests.cs:line 59

This is a regression from 3.6 and I suspect was introduced by #2239.
The right hand constraint of the And is getting evaluated against each item of the array instead of against the enumerable. I have tried stepping through and figuring out where things go wrong but without success.

I presume I am using the API correctly - I expected the assertion to check that the array contained donkey and did not contain mule. If I am wrong, I would appreciate some guidance on how to chain these constraints using the fluent API - or should one write 2 separate assertions?

[mikkelbu]

Before implementing a solution to this I think we should have tests that cover all the functionality of CollectionContainsConstraint - as it were in version 3.7 - and then use these tests to ensure that we have kept all the behaviour. I'll try to look into writing these tests tonight (if I have time). The tests should also cover #2412.

[mikkelbu]

I've tried to go through all the changes done in #2239 and write tests for each change. All the tests pass in version 3.7.1, but in 3.8.1:

• 5 does not compile (due to 'SomeItemsConstraint' does not contain a definition for 'Using'), and
• 3 fails with System.ArgumentException : The actual value must be an IEnumerable

https://gist.github.com/mikkelbu/370fe6a735c41906dca1fad28282f19e

[mikkelbu]

@rprouse I've added this issue to the 3.8.2 milestone.

[Snaaio]

I am currently using nunit.framework v3.9.0.0 and still have problems when using a Has.One.Member(...) constraint:
class TestElement { }

var element = new TestElement();
Assert.That(new System.Collections.Generic.List<TestElement> { element }, Has.One.Member(element));

Test fails with the following error:

Message: System.ArgumentException : Expected: IEnumerable But was: TestElement
Parameter name: actual

Does this mean this issue is not completely fixed, is it a new issue or am I doing something wrong?

[ChrisMaddock]

@Snaaio - would you file a new issue for this please? 🙂 I'm not entirely sure how the syntax should work here off the top of my head - is this a regression from a previous version of the framework?

[CharliePoole]

I'm suspicious of the syntax Has.One.Member, as opposed to simply Has.Member or even Has.One.SameAs. It could be we are letting an unimplemented sequence through when it should not be allowed - or should be implemented if it is allowed.

[mikkelbu]

@Snaaio As far as I can tell from the PR you can write the assertion as

Assert.That(new List<TestElement> { element }, Has.One.EqualTo(element));

But note that this will also be satisfied by a collection with more than one element, as long as exactly one element is equal to element. If you only want to match a collection with exactly one element that matches, then something like

Assert.That(new List<TestElement> { element, element2 }, Has.Member(element).And.Count.EqualTo(1));

can be used (note that I'm usually not using these long method sequences, so it can be that it can be written more succinct 😄 ).

@ChrisMaddock The Has.One syntax is new in 3.8 and is a short hand for Has.Exactly(1).Items (see #2004).