Your first expectation

This library will never be able to cope with all ideas and use cases. Therefore, it is possible to use the aweXpect.Core package and write your own extensions. This package aims to be more stable than the main aweXpect package, to reduce the risk of version conflicts between different extensions.

The samples on this page use the following namespaces:

using System.Diagnostics.CodeAnalysis;
using aweXpect.Core;
using aweXpect.Results;

Expectations

You can extend the expectations for any types, by adding extension methods on IThat<TType>.

If you want to verify that a string is an absolute path, you specify the following method signature:

/// <summary>
///     Verifies that the <paramref name="subject"/> is an absolute path.
/// </summary>
public static AndOrResult<string, IThat<string>> IsAbsolutePath(this IThat<string> subject)
{
    // ...
}

The result type decides how the expectation can continue: AndOrResult allows combining it with further expectations using .And and .Or.

ExpectationBuilder

The next step is to extract the ExpectationBuilder. In order to keep the automatic code suggestions for developers clear, you have to cast the IThat<TType> interface to IExpectThat<TType>, which will then give access to the ExpectationBuilder property. To improve readability you can copy the following internal extension method into your project:

[ExcludeFromCodeCoverage]
internal static IExpectThat<T> Get<T>(this IThat<T> subject)
{
    if (subject is IExpectThat<T> thatIs)
    {
        return thatIs;
    }

    throw new NotSupportedException("IThat<T> must also implement IExpectThat<T>");
}

You can then use the ExpectationBuilder to add an IsAbsolutePathConstraint:

public static AndOrResult<string, IThat<string>> IsAbsolutePath(this IThat<string> subject)
    => new(subject.Get().ExpectationBuilder.AddConstraint((it, grammars)
            => new IsAbsolutePathConstraint(it, grammars)),
        subject);

The factory receives the name of the subject (it) and the grammars of the sentence, which the constraint uses to write its part of the failure message. Constraints and results shows how to write the IsAbsolutePathConstraint, and message conventions how its texts should read.