Add feature to check if an XElement or XAttribute is absent within the XDocument

[skukshaus]

Background and motivation

Currently, there is an implementation to check whenever an Attribute or Element is within the Document: https://fluentassertions.com/xml/
However, sometimes it is necessary to check if those attributes are absent. Currently, there is no possibility to do this. Maybe it would be possible to use the HaveElement() Method and catch the Exception, but this feels dirty.

I think it could also be a good idea, to add a constraint if the attribute/element does not have a specific value

API Proposal

public class XElementAssertions
{
    public AndConstraint<XElementAssertions> NotHaveAttribute(string unexpectedAttribute, string because = "", params object[] becauseArgs);
    public AndConstraint<XElementAssertions> NotHaveAttribute(string unexpectedAttribute, string unexpectedValue, string because = "", params object[] becauseArgs);

    public AndWhichConstraint<XElementAssertions, XElement> NotHaveElement(string unexpectedElement, string because = "", params object[] becauseArgs);
    public AndWhichConstraint<XElementAssertions, XElement> NotHaveElement(string unexpectedElement, object unexpectedValue, string because = "", params object[] becauseArgs);
}

API Usage

var element = XElement.Parse("<user><forename>john</forename></user>");
element.Should().NotHaveElement("surname");


var element = XElement.Parse("<user><forename>john</forename><surname>doe</surname></user>");
element.Should().NotHaveElement("surname", "smith");



var element = XElement.Parse("<user forename='john' />");
element.Should().NotHaveAttribute("surname");


var element = XElement.Parse("<user forename='john' surname='doe' />");
element.Should().NotHaveAttribute("surname", "smith");

Alternative Designs

No response

Risks

No response

Are you willing to help with a proof-of-concept (as PR in that or a separate repo) first and as pull-request later on?

Yes, please assign this issue to me.

[dennisdoomen]

Sure, makes sense. What do you think @jnyrup ?

[jnyrup]

It certainly makes sense to have more negated assertions for XML types 👍

You suggest adding an overload of NotHaveElement having an object unexpectedValue, but we don't currently have an affirmative HaveElement(string expectedElement, object expectedValue).
So I'm not sure we should add that overload.

We currently have HaveElement(string expectedName) on

• XDocumentAssertions
• XElementAssertions
• XmlElementAssertions

and HaveAttribute(string expectedName, string expectedValue) on

• XElementAssertions
• XmlElementAssertions

In order to have a consistent API, it would be be nice to add the proposed methods on all relevant classes.

[skukshaus]

Hey @jnyrup and @dennisdoomen

Thanks for the reply, should I implement the changes according to your guidelines and create another PR?
I mean, including the overloads for the other use cases as well.

(I mean, I really need this extension because I have a dirty workaround for my problem (I've added a Must<XElementAssertions>() method because Should<XElementAssertions>() is already there).)

BG Sergej

[dennisdoomen]

Thanks for the reply, should I implement the changes according to your guidelines and create another PR?

Everything that is in this proposal should be delivered as a consistent set of changes. And to prevent contributors from abandoning the work after the first PR, we need to insist on contributors to provide a PR that covers everything that is needed to maintain that consistency. Hope you understand.

[dennisdoomen]

It took me a couple of seconds to realize that element.Should().NotHaveElement("surname", "smith"); meant that element should not have an element with a specific value. I guess that also means that if element has element surname with a different value, it is okay? If so, then I think we should call it NotHaveElementWithValue.

In that case, we need:

• XDocumentAssertions.HaveElementWithValue

• XDocumentAssertions.NotHaveElementWithValue

• XDocumentAssertions.NotHaveElement

• XElementAssertions.HaveElementWithValue

• XElementAssertions.NotHaveElementWithValue

• XElementAssertions.NotHaveElement

• XElementAssertions.HaveAttributeWithValue

• XElementAssertions.NotHaveAttributeWithValue

• XElementAssertions.NotHaveAttribute

To be clear, you can only add the NotHaveElementWithValue if you also include HaveElementWithValue

XmlElementAssertions are out of scope as far as I'm concerned.