It's a bad idea to have constraints fail when they are used improperly. If you do that then...
Constraint c = new NonReusableConstraint(...); Assert.That( actual, c ); // This fails Assert.That( actual, new NotConstrant( c ) ); // This succeeds! In an earlier version of NUnit we had this problem when using a constraint that expects a collection with a non-collection. The constraint was failing but its negation would succeed. Now we throw an ArgumentException in this sort of situation. In the case of a non-reusable constraint we could throw an exception, but only if the constraint "knew" it was being reused. Charlie > -----Original Message----- > From: > nunit-core-bounces+charlie=nunit....@lists.launchpad.net > [mailto:nunit-core-bounces+charlie=nunit....@lists.launchpad.n > et] On Behalf Of blaz > Sent: Friday, March 05, 2010 3:16 AM > To: nunit-core@lists.launchpad.net > Subject: [Nunit-core] [Bug 532488] Re: constraintsfrom > ConstraintExpression/ConstraintBuilder are not reusable > > In some rare cases reuse could be useful. > Main problem is that I was unable to find any documentation > specifying that constraints should not be reused, or that > constrains supplied by NUnit are not reusable. Actually in > most cases under most conditions constraints are reusable. > > I think that this bug could be fixed either by making > constrains reusable or by placing appropriate warning in > documentation > (http://www.nunit.org/index.php?p=constraintModel&r=2.5.3), > or constrains that are not reusable should fail on reuse. > > -- > constraints from ConstraintExpression/ConstraintBuilder are > not reusable > https://bugs.launchpad.net/bugs/532488 > You received this bug notification because you are a member > of NUnit Developers, which is subscribed to NUnit V2. > > Status in NUnit V2 Test Framework: New > > Bug description: > Constraint that I receive from syntax helper (Is.Not.Null) is > not reusable, but I guess this is more general problem. > I found this problem when upgrading nunit.framework.dll from > v2.4.6 to v.2.5.3. In both cases tests were executed witn > NUnit 2.5.3 console. > Worst thing about this problem seems that tests could > actually pass when they should fail if you reuse constraint. > > Here is simple example that demonstrates the problem: > > using NUnit.Framework; > using NUnit.Framework.Constraints; > > namespace NUnit_2_5_3_bug > { > [TestFixture] > public class FailToReuseConstraint > { > /// <summary> > /// Constraint from <see cref="ConstraintExpression"/>. > /// </summary> > /// <remarks> > /// Demonstrates that constraint received from syntax > helper is not reusable. > /// </remarks> > [Test] > public void FromSyntaxHelper() > { > Constraint expression = Is.Not.Null; > Assert.That(this, expression, "one"); > Assert.That(this, expression, "two"); // this > step fails on NUnit.2.5.3 > } > > /// <summary> > /// How NUnit 2.4 did it (i think). > /// </summary> > [Test] > public void NotConstraint() > { > Constraint expression = new NotConstraint(Is.Null); > Assert.That(this, expression, "one"); > Assert.That(this, expression, "two"); > } > } > } > > > > _______________________________________________ > Mailing list: https://launchpad.net/~nunit-core > Post to : nunit-core@lists.launchpad.net > Unsubscribe : https://launchpad.net/~nunit-core > More help : https://help.launchpad.net/ListHelp > _______________________________________________ Mailing list: https://launchpad.net/~nunit-core Post to : nunit-core@lists.launchpad.net Unsubscribe : https://launchpad.net/~nunit-core More help : https://help.launchpad.net/ListHelp
