Aksio.Specifications 1.4.3

Specifications

This project represents a way to do Specification by Example - BDD style inspired by the conciseness of Machine.Specifications. The motivation behind is years of work with Machine.Specifications and the wish to maintain the approach, structure and syntax - but get more love from tooling across different platforms and IDEs and editors; read more here.

What does it do?

In BDD one talks about the given, when, then. Much like arrange, act and assert in a way that is more common in TDD. The biggest difference is on a mindset level of thinking in specifications of behaviors in your system. What this particular library delivers is a way to do these and also keep in line with what is common in the BDD world of having isolated specifications and not have typically a FooTests and dump all your tests for the unit Foo in it.

The library supports my convention lifecycle methods Establish(), Because() and Destroy(). There is no virtual method to override, just match the expected signatures:

If your specification requires to run in an async context, it also supports the following:

All lifecycle methods are optional and will be ignored if not there. Multiple levels of inheritance recursively is supported, meaning that specifications will run all the lifecycle methods from the lowest level in the hierarchy chain and up the hierarchy (e.g. no_user_authenticated → when_authenticating_a_null_user).

To get all this to work, all you need to do is inherit from the Specification type found in Aksio.Specifications.

Structure and naming

The general purpose of BDD and specification by example is to make it all very human readable and possible to navigate quite easily. New developers can come into the solution and pretty much read up on the specifications and get a glimpse of how the system works. So rather than having a FooTests class with all the tests, it is recommended to have folders describing the scenario being specified. For a unit this could be named for_<name of unit> e.g. : for_SecurityService. If you're testing a more domain centric scenario in your system that involves multiple units, the folder name would reflect the name of the scenario e.g.: for_logging_in_users.

Within these folders you'd keep your when statements. E.g. When_authenticating_an_admin_user. If you want to group things, for instance lets say you have multiple behaviors within the concept of authenticating, you could then have a folder grouping these called When_authenticating and then drop in the behavior specifications within this folder an_admin_user and a_null_user.

In addition to this you might want to reuse a context. This can quite easily be achieved through inheritance. Structure-wise you'd then have a given folder and namespace where you'd put the common reusable context - again reflecting what it represents, for instance for our authentication scenario: no_user_authenticated.

For a sample of how this looks like, look within the sample folder.

Compiler Warnings

Since the naming of classes, methods and structure deviates from what is expected by default from the C# compiler, you typically end up getting a lot of warnings. These can be turned off by adding a NoWarn element within a PropertyGroup to your .csproj file:

<PropertyGroup>
    <NoWarn>CA1707;CS1591;RCS1213;IDE0051;IDE1006;CA1051</NoWarn>
</PropertyGroup>

Example

In the sample folder you'll find samples of using it. Basically, building on the Machine.Specifications sample - this would become:

class When_authenticating_an_admin_user : Specification
{
    SecurityService subject;
    UserToken user_token;

    void Establish() =>
             subject = new SecurityService();

    void Because() =>
             user_token = subject.Authenticate("username", "password");

    [Fact] void should_indicate_the_users_role() =>
        user_token.Role.ShouldEqual(Roles.Admin);

    [Fact] void should_have_a_unique_session_id() =>
        user_token.SessionId.ShouldNotBeNull();
}

Catching an exception and testing for the correct exception:

class When_authenticating_a_null_user : Specification
{
    SecurityService subject;
    Exception result;

    void Establish() =>
             subject = new SecurityService();

    void Because() =>
             result = Catch.Exception(() => subject.Authenticate(null, null));

    [Fact] void should_throw_user_must_be_specified_exception() =>
        result.ShouldBeOfExactType<UserMustBeSpecified>();
}

Building reusable contexts (in a sub-namespace with given):

class no_user_authenticated
{
    protected SecurityService subject;

    void Establish() =>
             subject = new SecurityService();
}

Refactor one of the specifications:

class When_authenticating_a_null_user : given.no_user_authenticated
{
    Exception result;

    void Because() =>
             result = Catch.Exception(() => subject.Authenticate(null, null));

    [Fact] void should_throw_user_must_be_specified_exception() =>
        result.ShouldBeOfExactType<UserMustBeSpecified>();
}

Supports teardown through destroy:

class no_user_authenticated
{
    protected SecurityService subject;

    void Establish() =>
             subject = new SecurityService();

    void Destroy() => subject.Dispose();

}