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FakeItEasy configuration order: a pitfall in CQRS tests
Marco Franssen
4 min read•727 words
The project I'm currently working on uses CQRS and the ncqrs framework. Today, I reached a point where I needed to mock some of my domain services. I chose FakeItEasy and started by adding a reference to my DomainScenario project through a NuGet package.
In some of my more complex scenarios, I ran into an issue that took about 45 minutes to fix in one test. I then had to apply the same trick to the other failing tests.
Before I explain the issue with FakeItEasy, I should mention that I use my aggregate roots to prepare the event store. The problem is related to this particular setup.
For example, I have a Participant aggregate root like this:
public class Participant : BisAggregateRoot
{
private readonly IUniqueParticipantNrGuard _uniqueFormattedParticipantNrVerifier = NcqrsEnvironment.Get<IUniqueParticipantNrGuard>();
//other members left for convenience
private string _participantNrFormat;
private int _participantNr;
private Gender _gender;
private PartialDate _birthDate;
private string _remark;
public Guid ParticipantId { get { return EventSourceId; } }
// ReSharper disable UnusedMember.Local
private Participant()
// ReSharper restore UnusedMember.Local
{
}
public Participant(Guid participantId, ScientificStudy scientificStudy, string participantNrFormat, int participantNr, Gender gender, PartialDate birthdate)
: base(participantId)
{
_uniqueFormattedParticipantNrVerifier.GuardIsUnique(scientificStudy.ScientificStudyId, participantId,
string.Format(participantNrFormat, participantNr));
ApplyEvent(new ParticipantAddedEvent(Credentials)
{
ParticipantId = participantId,
ParticipantNrFormat = participantNrFormat,
ParticipantNr = participantNr,
ScientificStudyId = scientificStudy.ScientificStudyId,
Gender = gender.ActualValue,
Birthdate = birthdate.ActualValue
});
}
public void Edit(ScientificStudy scientificStudy, string participantNrFormat, int participantNr, Gender gender, PartialDate birthdate, string remark)
{
//Some other business rules
_uniqueFormattedParticipantNrVerifier.GuardIsUnique(scientificStudy.ScientificStudyId, ParticipantId,
string.Format(participantNrFormat, participantNr));
//Some other business rules
ApplyEvent(new ParticipantEditedEvent(Credentials)
{
ParticipantId = ParticipantId,
ParticipantNrFormat = participantNrFormat,
ParticipantNr = participantNr,
Gender = gender.ActualValue,
Birthdate = birthdate.ActualValue
});
}
protected void OnParticipantAdded(ParticipantAddedEvent e)
{
_claimedAliquots = new List<ClaimedAliquot>();
_participantNrFormat = e.ParticipantNrFormat;
_participantNr = e.ParticipantNr;
_gender = new Gender(e.Gender);
_birthDate = new PartialDate(e.Birthdate);
}
protected void OnParticipantEdited(ParticipantEditedEvent e)
{
_participantNrFormat = e.ParticipantNrFormat;
_participantNr = e.ParticipantNr;
_gender = new Gender(e.Gender);
_birthDate = new PartialDate(e.Birthdate);
_remark = e.Remark;
}
}As you can see, both the constructor and the edit method use the same domain service to check whether the participant number is unique. Keep this in mind: it's important because of how I prepare my event store.
To prepare the event store, I use a fluent builder I wrote that uses domain objects to generate the events.
public static class New
{
public static ScientificStudy ScientificStudy(string nr = "M001", string name = "Maastricht Study", string participantNrFormat = "P{0}", string boxNameFormat = "B{0}")
{
return new ScientificStudy(Default.Id.For.ScientificStudy, nr, name, participantNrFormat, boxNameFormat);
}
public static Participant Participant(ScientificStudy scientificStudy, string participantNrFormat = "P{0}", int participantNr = 1, int gender = 0, string birthdate = "19861117")
{
var realGender = new Gender(gender);
var realBirthDate = new PartialDate(birthdate);
return new Participant(Default.Id.For.Participant, scientificStudy, participantNrFormat, participantNr, realGender, realBirthDate);
}
//other members left for convenience
}Here's how I use this builder in my tests. Notice that GetChanges is an extension method on my aggregate roots.
protected override void SetupDependencies()
{
base.SetupDependencies();
var eventStore = NcqrsEnvironment.Get<IEventStore>();
var scientificStudy = New.ScientificStudy();
var scientificStudyEvent = scientificStudy.TrackChanges().GetChanges();
var participantEvents = New.Participant(scientificStudy).GetChanges();
eventStore.Store(Prepare.Events(scientificStudyEvent).ForSourceUncomitted(Default.Id.For.ScientificStudy, Default.Id.Random()));
eventStore.Store(Prepare.Events(participantEvents).ForSourceUncomitted(Default.Id.For.Participant, Default.Id.Random()));
}Initially, I registered my fakes as shown below, which made the test fail. I'm trying to check whether editing a participant throws a 'FormattedParticipantNrShouldBeUniqueException' when the participantNr is changed to one that already exists.
protected override void RegisterFakesInConfiguration(EnvironmentConfigurationWrapper configuration)
{
var commandService = new CommandService();
commandService.RegisterExecutor(new EditParticipantCommandExecutor());
var uniqueParticipantGuard = A.Fake<IUniqueParticipantNrGuard>();
A.CallTo(uniqueParticipantGuard).DoesNothing().Once();
A.CallTo(uniqueParticipantGuard).Throws(
new FormattedParticipantNrShouldBeUniqueException(_formattedParticipantNr));
configuration.Register<ICommandService>(commandService);
configuration.Register(uniqueParticipantGuard);
//other fakes left for convenience
base.RegisterFakesInConfiguration(configuration);
}After 45 minutes of searching and discussing it with my colleague, we found a solution.
protected override void RegisterFakesInConfiguration(EnvironmentConfigurationWrapper configuration)
{
var commandService = new CommandService();
commandService.RegisterExecutor(new EditParticipantCommandExecutor());
var uniqueParticipantGuard = A.Fake<IUniqueParticipantNrGuard>();
A.CallTo(uniqueParticipantGuard).Throws(
new FormattedParticipantNrShouldBeUniqueException(_formattedParticipantNr));
A.CallTo(uniqueParticipantGuard).DoesNothing().Once();
configuration.Register<ICommandService>(commandService);
configuration.Register(uniqueParticipantGuard);
//other fakes left for convenience
base.RegisterFakesInConfiguration(configuration);
}As you can see, the solution was simple, but hard to find: debugging didn't reveal that the configuration order was the issue.
Just switch the order in which you configure the mocked/faked object.
Last but not least, here's my actual test method.
[Then]
public void it_should_throw_an_formatted_participant_nr_should_be_unique_exception_containing_the_formatted_participant_nr()
{
var exception = (FormattedParticipantNrShouldBeUniqueException)CaughtException;
exception.FormattedParticipantNr.Should().Be(_formattedParticipantNr);
}I'm not sure whether I was doing it wrong or whether FakeItEasy needs a fix to prevent this issue. I hope I've explained it clearly and saved you some time if you encounter the same problem.
