问题
I've just started to use AutoFixture.AutoMoq in my unit tests and I'm finding it very helpful for creating objects where I don't care about the specific value. After all, anonymous object creation is what it is all about.
What I'm struggling with is when I care about one or more of the constructor parameters. Take ExampleComponent below:
public class ExampleComponent
{
public ExampleComponent(IService service, string someValue)
{
}
}
I want to write a test where I supply a specific value for someValue but leave IService to be created automatically by AutoFixture.AutoMoq.
I know how to use Freeze on my IFixture to keep hold of a known value that will be injected into a component but I can't quite see how to supply a known value of my own.
Here is what I would ideally like to do:
[TestMethod]
public void Create_ExampleComponent_With_Known_SomeValue()
{
// create a fixture that supports automocking
IFixture fixture = new Fixture().Customize(new AutoMoqCustomization());
// supply a known value for someValue (this method doesn't exist)
string knownValue = fixture.Freeze<string>("My known value");
// create an ExampleComponent with my known value injected
// but without bothering about the IService parameter
ExampleComponent component = this.fixture.Create<ExampleComponent>();
// exercise component knowning it has my known value injected
...
}
I know I could do this by calling the constructor directly but this would no longer be anonymous object creation. Is there a way to use AutoFixture.AutoMock like this or do I need to incorporate a DI container into my tests to be able to do what I want?
EDIT:
I probably should have been less absract in my original question so here is my specific scenario.
I have an ICache interface which has generic TryRead<T> and Write<T> methods:
public interface ICache
{
bool TryRead<T>(string key, out T value);
void Write<T>(string key, T value);
// other methods not shown...
}
I'm implementing a CookieCache where ITypeConverter handles converting objects to and from strings and lifespan is used to set the expiry date of a cookie.
public class CookieCache : ICache
{
public CookieCache(ITypeConverter converter, TimeSpan lifespan)
{
// usual storing of parameters
}
public bool TryRead<T>(string key, out T result)
{
// read the cookie value as string and convert it to the target type
}
public void Write<T>(string key, T value)
{
// write the value to a cookie, converted to a string
// set the expiry date of the cookie using the lifespan
}
// other methods not shown...
}
So when writing a test for the expiry date of a cookie, I care about the lifespan but not so much about the converter.
回答1:
You have to replace:
string knownValue = fixture.Freeze<string>("My known value");
with:
fixture.Inject("My known value");
You can read more about Inject here.
Actually the Freeze extension method does:
var value = fixture.Create<T>();
fixture.Inject(value);
return value;
Which means that the overload you used in the test actually called Create<T> with a seed: My known value resulting in "My known value4d41f94f-1fc9-4115-9f29-e50bc2b4ba5e".
回答2:
So I'm sure people could work out the generalized implementation of Mark's suggestion but I thought I'd post it for comments.
I've created a generic ParameterNameSpecimenBuilder based on Mark's LifeSpanArg:
public class ParameterNameSpecimenBuilder<T> : ISpecimenBuilder
{
private readonly string name;
private readonly T value;
public ParameterNameSpecimenBuilder(string name, T value)
{
// we don't want a null name but we might want a null value
if (string.IsNullOrWhiteSpace(name))
{
throw new ArgumentNullException("name");
}
this.name = name;
this.value = value;
}
public object Create(object request, ISpecimenContext context)
{
var pi = request as ParameterInfo;
if (pi == null)
{
return new NoSpecimen(request);
}
if (pi.ParameterType != typeof(T) ||
!string.Equals(
pi.Name,
this.name,
StringComparison.CurrentCultureIgnoreCase))
{
return new NoSpecimen(request);
}
return this.value;
}
}
I've then defined a generic FreezeByName extension method on IFixture which sets the customization:
public static class FreezeByNameExtension
{
public static void FreezeByName<T>(this IFixture fixture, string name, T value)
{
fixture.Customizations.Add(new ParameterNameSpecimenBuilder<T>(name, value));
}
}
The following test will now pass:
[TestMethod]
public void FreezeByName_Sets_Value1_And_Value2_Independently()
{
//// Arrange
IFixture arrangeFixture = new Fixture();
string myValue1 = arrangeFixture.Create<string>();
string myValue2 = arrangeFixture.Create<string>();
IFixture sutFixture = new Fixture();
sutFixture.FreezeByName("value1", myValue1);
sutFixture.FreezeByName("value2", myValue2);
//// Act
TestClass<string> result = sutFixture.Create<TestClass<string>>();
//// Assert
Assert.AreEqual(myValue1, result.Value1);
Assert.AreEqual(myValue2, result.Value2);
}
public class TestClass<T>
{
public TestClass(T value1, T value2)
{
this.Value1 = value1;
this.Value2 = value2;
}
public T Value1 { get; private set; }
public T Value2 { get; private set; }
}
回答3:
You could do something like this. Imagine that you want to assign a particular value to the TimeSpan argument called lifespan.
public class LifespanArg : ISpecimenBuilder
{
private readonly TimeSpan lifespan;
public LifespanArg(TimeSpan lifespan)
{
this.lifespan = lifespan;
}
public object Create(object request, ISpecimenContext context)
{
var pi = request as ParameterInfo;
if (pi == null)
return new NoSpecimen(request);
if (pi.ParameterType != typeof(TimeSpan) ||
pi.Name != "lifespan")
return new NoSpecimen(request);
return this.lifespan;
}
}
Imperatively, it could be used like this:
var fixture = new Fixture();
fixture.Customizations.Add(new LifespanArg(mySpecialLifespanValue));
var sut = fixture.Create<CookieCache>();
This approach can be generalized to some degree, but in the end, we're limited by the lack of a strongly typed way to extract a ParameterInfo from a particular constructor or method argument.
回答4:
I fee like @Nick was almost there. When overriding the constructor argument, it needs to be for the given type and have it limited to that type only.
First we create a new ISpecimenBuilder that looks at the "Member.DeclaringType" to keep the correct scope.
public class ConstructorArgumentRelay<TTarget,TValueType> : ISpecimenBuilder
{
private readonly string _paramName;
private readonly TValueType _value;
public ConstructorArgumentRelay(string ParamName, TValueType value)
{
_paramName = ParamName;
_value = value;
}
public object Create(object request, ISpecimenContext context)
{
if (context == null)
throw new ArgumentNullException("context");
ParameterInfo parameter = request as ParameterInfo;
if (parameter == null)
return (object)new NoSpecimen(request);
if (parameter.Member.DeclaringType != typeof(TTarget) ||
parameter.Member.MemberType != MemberTypes.Constructor ||
parameter.ParameterType != typeof(TValueType) ||
parameter.Name != _paramName)
return (object)new NoSpecimen(request);
return _value;
}
}
Next we create an extension method to allow us to easily wire it up with AutoFixture.
public static class AutoFixtureExtensions
{
public static IFixture ConstructorArgumentFor<TTargetType, TValueType>(
this IFixture fixture,
string paramName,
TValueType value)
{
fixture.Customizations.Add(
new ConstructorArgumentRelay<TTargetType, TValueType>(paramName, value)
);
return fixture;
}
}
Now we create two similar classes to test with.
public class TestClass<T>
{
public TestClass(T value1, T value2)
{
Value1 = value1;
Value2 = value2;
}
public T Value1 { get; private set; }
public T Value2 { get; private set; }
}
public class SimilarClass<T>
{
public SimilarClass(T value1, T value2)
{
Value1 = value1;
Value2 = value2;
}
public T Value1 { get; private set; }
public T Value2 { get; private set; }
}
Finally we test it with an extension of the original test to see that it will not override similarly named and typed constructor arguments.
[TestFixture]
public class AutoFixtureTests
{
[Test]
public void Can_Create_Class_With_Specific_Parameter_Value()
{
string wanted = "This is the first string";
string wanted2 = "This is the second string";
Fixture fixture = new Fixture();
fixture.ConstructorArgumentFor<TestClass<string>, string>("value1", wanted)
.ConstructorArgumentFor<TestClass<string>, string>("value2", wanted2);
TestClass<string> t = fixture.Create<TestClass<string>>();
SimilarClass<string> s = fixture.Create<SimilarClass<string>>();
Assert.AreEqual(wanted,t.Value1);
Assert.AreEqual(wanted2,t.Value2);
Assert.AreNotEqual(wanted,s.Value1);
Assert.AreNotEqual(wanted2,s.Value2);
}
}
回答5:
This seems to be the most comprehensive solution set here. So I'm going to add mine:
The first thing to create ISpecimenBuilder that can handle multiple constructor parameters
internal sealed class CustomConstructorBuilder<T> : ISpecimenBuilder
{
private readonly Dictionary<string, object> _ctorParameters = new Dictionary<string, object>();
public object Create(object request, ISpecimenContext context)
{
var type = typeof (T);
var sr = request as SeededRequest;
if (sr == null || !sr.Request.Equals(type))
{
return new NoSpecimen(request);
}
var ctor = type.GetConstructors(BindingFlags.Instance | BindingFlags.Public).FirstOrDefault();
if (ctor == null)
{
return new NoSpecimen(request);
}
var values = new List<object>();
foreach (var parameter in ctor.GetParameters())
{
if (_ctorParameters.ContainsKey(parameter.Name))
{
values.Add(_ctorParameters[parameter.Name]);
}
else
{
values.Add(context.Resolve(parameter.ParameterType));
}
}
return ctor.Invoke(BindingFlags.CreateInstance, null, values.ToArray(), CultureInfo.InvariantCulture);
}
public void Addparameter(string paramName, object val)
{
_ctorParameters.Add(paramName, val);
}
}
Then create extension method that simplifies usage of created builder
public static class AutoFixtureExtensions
{
public static void FreezeActivator<T>(this IFixture fixture, object parameters)
{
var builder = new CustomConstructorBuilder<T>();
foreach (var prop in parameters.GetType().GetProperties())
{
builder.Addparameter(prop.Name, prop.GetValue(parameters));
}
fixture.Customize<T>(x => builder);
}
}
And usage:
var f = new Fixture();
f.FreezeActivator<UserInfo>(new { privateId = 15, parentId = (long?)33 });
回答6:
Good thread, I added another twist based on many of the aswers already posted:
Usage
Example:
var sut = new Fixture()
.For<AClass>()
.Set("value1").To(aInterface)
.Set("value2").ToEnumerableOf(22, 33)
.Create();
Test classes:
public class AClass
{
public AInterface Value1 { get; private set; }
public IEnumerable<int> Value2 { get; private set; }
public AClass(AInterface value1, IEnumerable<int> value2)
{
Value1 = value1;
Value2 = value2;
}
}
public interface AInterface
{
}
Full test
public class ATest
{
[Theory, AutoNSubstituteData]
public void ATestMethod(AInterface aInterface)
{
var sut = new Fixture()
.For<AClass>()
.Set("value1").To(aInterface)
.Set("value2").ToEnumerableOf(22, 33)
.Create();
Assert.True(ReferenceEquals(aInterface, sut.Value1));
Assert.Equal(2, sut.Value2.Count());
Assert.Equal(22, sut.Value2.ElementAt(0));
Assert.Equal(33, sut.Value2.ElementAt(1));
}
}
Infrastructure
Extension method:
public static class AutoFixtureExtensions
{
public static SetCreateProvider<TTypeToConstruct> For<TTypeToConstruct>(this IFixture fixture)
{
return new SetCreateProvider<TTypeToConstruct>(fixture);
}
}
Classes participating in the fluent style:
public class SetCreateProvider<TTypeToConstruct>
{
private readonly IFixture _fixture;
public SetCreateProvider(IFixture fixture)
{
_fixture = fixture;
}
public SetProvider<TTypeToConstruct> Set(string parameterName)
{
return new SetProvider<TTypeToConstruct>(this, parameterName);
}
public TTypeToConstruct Create()
{
var instance = _fixture.Create<TTypeToConstruct>();
return instance;
}
internal void AddConstructorParameter<TTypeOfParam>(ConstructorParameterRelay<TTypeToConstruct, TTypeOfParam> constructorParameter)
{
_fixture.Customizations.Add(constructorParameter);
}
}
public class SetProvider<TTypeToConstruct>
{
private readonly string _parameterName;
private readonly SetCreateProvider<TTypeToConstruct> _father;
public SetProvider(SetCreateProvider<TTypeToConstruct> father, string parameterName)
{
_parameterName = parameterName;
_father = father;
}
public SetCreateProvider<TTypeToConstruct> To<TTypeOfParam>(TTypeOfParam parameterValue)
{
var constructorParameter = new ConstructorParameterRelay<TTypeToConstruct, TTypeOfParam>(_parameterName, parameterValue);
_father.AddConstructorParameter(constructorParameter);
return _father;
}
public SetCreateProvider<TTypeToConstruct> ToEnumerableOf<TTypeOfParam>(params TTypeOfParam[] parametersValues)
{
IEnumerable<TTypeOfParam> actualParamValue = parametersValues;
var constructorParameter = new ConstructorParameterRelay<TTypeToConstruct, IEnumerable<TTypeOfParam>>(_parameterName, actualParamValue);
_father.AddConstructorParameter(constructorParameter);
return _father;
}
}
Constructor parameter relay from other answers:
public class ConstructorParameterRelay<TTypeToConstruct, TValueType> : ISpecimenBuilder
{
private readonly string _paramName;
private readonly TValueType _paramValue;
public ConstructorParameterRelay(string paramName, TValueType paramValue)
{
_paramName = paramName;
_paramValue = paramValue;
}
public object Create(object request, ISpecimenContext context)
{
if (context == null)
throw new ArgumentNullException(nameof(context));
ParameterInfo parameter = request as ParameterInfo;
if (parameter == null)
return new NoSpecimen();
if (parameter.Member.DeclaringType != typeof(TTypeToConstruct) ||
parameter.Member.MemberType != MemberTypes.Constructor ||
parameter.ParameterType != typeof(TValueType) ||
parameter.Name != _paramName)
return new NoSpecimen();
return _paramValue;
}
}
来源：https://stackoverflow.com/questions/16819470/autofixture-automoq-supply-a-known-value-for-one-constructor-parameter