Is it possible to assign a fixed value to a property on a child instance when building a parent with Autofixture? It will add default values to all the properties on the child instance like a charm, but I would like to override and assign a specific value to one of the properties on the child instance.
Given this parent/child relationship:
public class Person
{
public string FirstName { get; set; }
public string LastName { get; set; }
public Address Address { get; set; }
}
public class Address
{
public string Street { get; set; }
public int Number { get; set; }
public string City { get; set; }
public string PostalCode { get; set; }
}
I would like to assign a specific value to the City property on the address instance. I was thinking in the lines of this test code:
var fixture = new Fixture();
var expectedCity = "foo";
var person = fixture
.Build<Person>()
.With(x => x.Address.City, expectedCity)
.Create();
Assert.AreEqual(expectedCity, person.Address.City);
That is not possible. I guess, by the reflection exception
System.Reflection.TargetException : Object does not match target type.
...that Autofixture tries to assign the value to a City property on the Person instance instead of an Address instance.
Any suggestions?
And yes, I know that I could just add an extra step like the following:
var fixture = new Fixture();
var expectedCity = "foo";
// extra step begin
var address = fixture
.Build<Address>()
.With(x => x.City, expectedCity)
.Create();
// extra step end
var person = fixture
.Build<Person>()
.With(x => x.Address, address)
.Create();
Assert.AreEqual(expectedCity, person.Address.City);
...but was hoping for the first version or something similar (fewer steps, more terse).
Note: I'm using Autofixture v3.22.0
For completeness, here's another way to do it:
fixture.Customize<Address>(c =>
c.With(addr => addr.City, "foo"));
var person = fixture.Create<Person>();
This will customize the creation of all instances of Address
If you end up using this often enough, it may be worthwhile wrapping it inside an ICustomization
:
public class AddressConventions : ICustomization
{
public void Customize(IFixture fixture)
{
fixture.Customize<Address>(c =>
c.With(addr => addr.City, "foo"));
}
}
fixture.Customize(new AddressConventions());
Not to be dismissive of the question, but the simplest solution might actually be this:
[Fact]
public void SimplestThingThatCouldPossiblyWork()
{
var fixture = new Fixture();
var expectedCity = "foo";
var person = fixture.Create<Person>();
person.Address.City = expectedCity;
Assert.Equal(expectedCity, person.Address.City);
}
Assignment of explicit values to properties is something most languages already excel at (C# certainly does), so I don't think AutoFixture needs a complicated DSL to reproduce half of that functionality.
You can use a Do method on the builder:
var person = this.fixture
.Build<Person>()
.Do( x => x.Address.City = expectedCity )
.Create();
You can also inject and freeze your instance to the fixture:
this.fixture.Inject( expectedCity );
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