Working sample of Custom Constraints.

[constructor]

Hi,

I am looking for working sample of custom constraints. Unfortunately, page http://www.nunit.org/index.php?p=customConstraints&r=2.5.10 doesn't contain sample. 

I investigate "custom constraints" and prepare next test:

[Test]
        public void Strings_MyConstraint()
        {
            const string expected = "Joe";
            const string actual = "joe";
            var myConstraint = new MyConstraint(expected);
            Assert.That(actual, Has.Some.Matches(myConstraint));
        }

where debug version of MyConstraint:

public class MyConstraint : Constraint
    {
        private readonly object m_expected;        
        public MyConstraint(object expectedValue)
        {
            m_expected = expectedValue;
        }
        #region Implementation of abstract methods
        public override bool Matches(object actual)
        {
            return false;            
            //return ((string)m_expected).ToLower() == ((string)actual).ToLower();
        }
        public override void WriteDescriptionTo(MessageWriter writer)
        {
            throw new NotImplementedException();
        }
        #endregion
    }

and actual parameter contains first symbol of actual value:

Please, could you publish working sample of custom constraint?

I use nunit 2.6.3.

I check option to implement "deep" compare of 2 objects and want to check "custom constraint" for the implementation.

thank you,

Igor.

[Simone Busoli]

Hi Igor,

you can check out how NUnit's own constraints are implemented here.

For a simple, self-contained example I would suggest the XmlSerializableConstraint.

Simone

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[constructor]

Hi Simone,

Unfortunately, I cannot understand the sample.

Could you implement simple constrain (compare 2 strings with ignoring lower/upper case)?

For any other type, let constrain raise error.

thank you,

Igor.

[Simone Busoli]

Such a constraint already exists:

Assert.That(actual, Is.EqualTo(expected).Ignor

​e​

Case)

​

[constructor]

I understand, but I want to see simple sample for customer constraint.

[Simone Busoli]

Igor, I already pointed you at the repository where you can find plenty of them, I'm afraid there nothing else I can help you with.

Simone

[Charlie Poole]

Hi Igor,

If the example Simone suggested is too difficult because of how it deals with serialization look at some of the others. There are over 100 and I'm sure at least a few of them will help you. We plan to develop some examples for the new docs, but none of us have time to do it right in this thread.

Charlie

[constructor]

Charlie,

Let's define next task: I want sometimes to compare only even symbols in my strings with help of nunit and Is.EqualTo.

So, I prepare customer's constraint EvenCharsConstraint and implement next tests (see below).

But the tests contain 2 "expected" variables transfer: to original EqualTo and my OnlyEvenChars. How can I re-design the code to receive IsEqual as basis, OnlyEvenChars as extension via fluent interface and single "expected" transfer?

Current implementation ignores first IsEqualTo, but I don't understand how to use it in my customer EvenCharsConstraint.

        [Test]
        public void SameEvenChars_MyConstraint_Pass()
        {
            const string expected = "Tom";
            const string actual = "Joe";
            Assert.That(actual, Is.EqualTo(expected)
                                  .OnlyEvenChars(expected));
        }
        [Test]
        [ExpectedException(typeof(AssertionException))]
        public void NotSameEvenChars_MyConstraint_Failed()
        {
            const string expected = "Tom";
            const string actual = "Sam";
            Assert.That(actual, Is.EqualTo(expected)
                                  .OnlyEvenChars(expected));
        }

 

where class EvenCharsConstraint implemented next:

    public class EvenCharsConstraint : EqualConstraint
    {
        private readonly object m_expected;        
        private object m_actual;
        public EvenCharsConstraint(object expectedValue)
            : base(expectedValue)

        {
            m_expected = expectedValue;
        }
        #region Implementation of abstract methods
        public override bool Matches(object actual)
        {

            m_actual = actual;
            bool matches = base.Matches(actual);
            if (!matches && m_expected is String && m_actual is String)
            {
                string expectedString = (string) m_expected;
                string actualString = (string) actual;
                if (expectedString.Length == actualString.Length)
                {
                    bool result = !expectedString.Where((expectedChar, index) => (index + 1) % 2 == 0 && expectedChar != actualString[index]).Any();
                    matches = result;
                }
            }
            return matches;
        }
        #endregion
    }

    public static class MyIs
    {
        public static EqualConstraint OnlyEvenChars(this EqualConstraint equalConstraint, object expected)
        {
            return new EvenCharsConstraint(expected);
        }            
    }

thank you,

Igor.

[constructor]

Also implemented other version:

 [Test]
        public void SameEvenChars_MyConstraint_Pass()
        {
            const string expected = "Tom";
            const string actual = "Joe";
            Assert.That(actual, Is.EqualTo(expected)

                                  .OnlyEvenChars());
        }

with help of 

public class EvenCharsEqualityComparer : IEqualityComparer
    {
        public new bool Equals(object x, object y)
        {
            if (x is String && y is String)
            {
                string xString = x as String;
                string yString = y as String;
                bool result = (xString.Length == yString.Length);
                result = result && !yString.Where((expectedChar, index) => (index + 1) % 2 == 0 && expectedChar != xString[index]).Any();
                return result;
            }
            var equalConstraint = new EqualConstraint(y);
            return equalConstraint.Matches(x);
        }
        public int GetHashCode(object obj)
        {
            return base.GetHashCode();
        }
    }

Could you help me to understand correct patterns of "custom constraint" usage?

thank you,

Igor.