Xceed Logo
Shop
Fluent Assertions Documentation
In This Topic
    Basic Assertions
    In This Topic

    The following assertions are available to all types of objects.

    C#
    Copy Code 
    object theObject = null;
theObject.Should().BeNull("because the value is null");
theObject.Should().NotBeNull();

theObject = "whatever";
theObject.Should().BeOfType<string>("because a {0} is set", typeof(string));
theObject.Should().BeOfType(typeof(string), "because a {0} is set", typeof(string));

    Sometimes you might like to first assert that an object is of a certain type using BeOfType and then continue with additional assertions on the result of casting that object to the specified type. You can do that by chaining those assertions onto the Which property like this.

    C#
    Copy Code 
    someObject.Should().BeOfType<Exception>()
  .Which.Message.Should().Be("Other Message");

    To assert that two objects are equal (through their implementation of Object.Equals), use

    C#
    Copy Code 
    string otherObject = "whatever";
theObject.Should().Be(otherObject, "because they have the same values");
theObject.Should().NotBe(otherObject);

    To assert that an object is equal to one of the provided objects, you can use

    C#
    Copy Code 
    theObject.Should().BeOneOf(obj1, obj2, obj3);

    To assert object equality using a custom equality comparer, you can use

    C#
    Copy Code 
    theObject.Should().Be(otherObject, new ObjEqualityComparer());
theObject.Should().NotBe(otherObject, new ObjEqualityComparer());
theObject.Should().BeOneOf(new[] { obj1, obj2, obj3 }, new ObjEqualityComparer());

    If you want to make sure two objects are not just functionally equal but refer to the exact same object in memory, use the following two methods.

    C#
    Copy Code 
    theObject = otherObject;
theObject.Should().BeSameAs(otherObject);
theObject.Should().NotBeSameAs(otherObject);

    Other examples of some general purpose assertions include

    C#
    Copy Code 
    var ex = new ArgumentException();
ex.Should().BeAssignableTo<Exception>("because it is an exception");
ex.Should().NotBeAssignableTo<DateTime>("because it is an exception");

var dummy = new Object();
dummy.Should().Match(d => (d.ToString() == "System.Object"));
dummy.Should().Match<string>(d => (d == "System.Object"));
dummy.Should().Match((string d) => (d == "System.Object"));

    As an alternative to using predicate matching, it is also possible to use element inspectors to do nested assertions in a fluent way.

    C#
    Copy Code 
    var productDto = new ProductDto
{
    Name = "Some product name",
    Price = 19.95,
    SKU = "ABC12345",
    Store = new Store
    {
        Country = "Germany",
        Quantity = 42
    }
};

productDto.Should().Satisfy<ProductDto>(dto =>
{
    dto.Name.Should().Be("Some product name");
    dto.Price.Should().Be(19.95);
    dto.SKU.Should().EndWith("12345");
    dto.Store.Should().Satisfy<Store>(store =>
    {
        store.Country.Should().Be("Germany");
        store.Quantity.Should().BeGreaterThan(40);
    });
});

    Some users requested the ability to easily downcast an object to one of its derived classes in a fluent way.

    C#
    Copy Code 
    customer.Animals.First().As<Human>().Height.Should().Be(178);

    We’ve also added the possibility to assert that an object can be serialized and deserialized using the XML or data contract formatters.

    C#
    Copy Code 
    theObject.Should().BeXmlSerializable();
theObject.Should().BeDataContractSerializable();