Autofixture: Is it possible to create an instance based on a runtime `System.Type`?
For making sure my AutoMapper mappings don't blow up, I have a test class similar to the following:
public class MapperTests
{
private readonly IMapper _mapper; // from AutoMapper
private readonly IFixture _fixture;
public MapperTests()
{
_mapper = SetUpAutoMapper();
_fixture = new Fixture();
}
[Theory]
[InlineData(typeof(Foo), typeof(Bar))]
[InlineData(typeof(Boo), typeof(Far))]
// etc ...
public void CanMapTypes(Type inputType, Type outputType)
{
var input = _fixture.Create(inputType);
// throws exceptions if something's broken:
_mapper.Map(input, outputType)
}
}
I just discovered that _fixture.Create(inputType) doesn't actually create an instance of the type (e.g. a Foo in the first test) but actually an instance of System.Type. This, of course, renders my test fairly useless.
I looked through the available methods (just browsing IntelliSense) but couldn't find one that seemed to match my expectations. Is there a way to do what I want here; basically create an instance of a type provided at runtime?
tomasaschan
All 3 comments
It seems that I know what is going on 😄
If you try the AutoFixture v4, you will find that this code doesn't compile. The reason is that we extracted confusing Create() method overloads to a separate package, so only users who knows what they are doing should use them.
```c#
_fixture.Create(inputType);
It might look that you are making a request of `typeof(Foo)` here, however in reality you are passing this argument as a `seed` and the actual request type is `typeof(Type)`. To fix the issue please tune a bit your code:
```c#
public class Foo
{
}
[Theory]
[InlineData(typeof(Foo))]
public void TestTypeRequest(Type requestType)
{
var fixture = new Fixture();
var result = fixture.Create(requestType, new SpecimenContext(fixture));
Assert.IsAssignableFrom<Foo>(result);
}
API is probably not succinct, however your scenario is not common, so that should be fine.
Let me know whether that helped 😉
zvirja
on 16 Nov 2017
Thanks!
By reading the source code of the generic fixture.Create<T>() object, figuring out where it eventually ends up, I also found out that this works:
var input = new SpecimenContext(_fixture).Resolve(sourceType);
I guess they are more or less equivalent :) Thanks a lot!
tomasaschan
on 17 Nov 2017
@tlycken Indeed, both snippets do the same, while your option looks much better :) Will use it in future if needed :blush:
zvirja
on 17 Nov 2017
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Most helpful comment
Thanks!
By reading the source code of the generic
fixture.Create<T>()object, figuring out where it eventually ends up, I also found out that this works:I guess they are more or less equivalent :) Thanks a lot!