Nconstraints

In Part 1 we created a custom NUnit constraint but you where limited in using the constraint.  You could only write:

 
// Instantiate the constraint. 
Assert.That(expected, new EquivalentPropertyWiseToConstraint(actual)); 

// Matches syntax. 
Assert.That(expected, Is.Not.Matches(new EquivalentPropertyWiseToConstraint(actual)));

It would be nice to write:

// Directly access the constraint from Is.
Assert.That(expected, Is.EquivalentPropertyWiseTo(actual));

// Chain the constraint in Is.
Assert.That(expected, Is.Not.EquivalentPropertyWiseTo(actual));

To do that you should read the documentation.  End of blog post.

So is that joke still funny?  No, OK, no more.  Lets get back to what we are doing.  To access the method using Is you need to override the Is class and add a static method.  I recommended making the method name similar to your constraint name.  For example:

NUnit has has built in constraints for most the tests you will need to write so there is no need to create your own.  End of blog post.

OK, that was a bad joke.  The first step in creating a NUnit custom constraint is to read the documentation.  That’s it.  End of blog post.

Not as funny as the first time?  Not funny at all?  I won’t use that joke again.  But you did read the documentation right?  OK, good.

A common unit test assert I need to do is compare all the property values of one object to another.  For example:

[Test]
public void TestSaveWorks()
{
  // Create a value to save.
  var expectedDto = new SomeDto() {ValueOne = 1, ValueTwo = "Blah"};

  // Save the value.
  _someDbService.Save(dtoToSave);

  // Load the value from the database.  The DTO ID
  // should have been set by the save.
  var actualDto = _someDbService.Find(expectedDto.Id);
  
  Assert.That(expectedDto.ValueOne, Is.EqualTo(actualDto.ValueOne));
  Assert.That(expectedDto.ValueTwo, Is.EqualTo(actualDto.ValueTwo));
}

In this test we only have two properties to test but if the object has 10 plus properties to test that would be quite onerous.   I often forget to update the tests after I add a new property to the object.