SparkyTestHelpers: Mapping/AutoMapper

part of the “SparkyTestHelpers” suite of .NET unit testing tools…

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SparkyTestHelpers.Mapping: NuGet package | Source Code
SparkyTestHelpers.AutoMapper: NuGet package | Source Code

There aren’t many projects where you don’t have to “map” properties from one type to another. (I’m sorry if you’re a cartography fan who thought this would be about that kind of maps. 🗺)

Hand-written “destination.X = source.X;” code is a frequent source of bugs. It’s easy to accidentally code the wrong variable on one side or the other, or to miss properties. Tools like AutoMapper make it a lot easier to define mapping logic, but it’s still something that should be tested.

Wouldn’t it be nice if there was a unit testing tool that made map testing just as easy as AutoMapper makes mapping?

SparkyTestHelpers.Mapping

MapTester<TSource, TDestination>

class SparkyTestHelpers.Mapping.MapTester<TSource, TDestination>

This class is for testing that properties were successfully “mapped” from one type to another, using an AutoMapper-inspired fluent syntax (but your source/destination don’t have to be created via AutoMapper — It doesn’t care how the instances were created).

Methods

• MapTester<TSource, TDestination> WithLogging(Action<String> action)
  (optional) “Callback” action to log property values when asserting. If called without an action, defaults to Console.WriteLine.
• MapTester<TSource, TDestination> IgnoringMember(Expression<Func<TDestination, Object>> destExpression)
• MapMemberTester<TSource, TDestination> WhereMember(Expression<Func<TDestination, Object>> destExpression)
• void AssertMappedValues(TSource source, TDestination dest)
  throws exception if any source/destination map validation specifications fail, or if any destination properties aren’t either tested or IgnoreMember’d.

Static Methods

• MapTester<TSource, TDestination> ForMap()

Example

using SparkyTestHelpers.Mapping;
...
    Foo foo = CreateAndPopulateTestFoo();
    Bar bar = Mapper.Map<Foo, Bar>(foo); 
    MapTester.ForMap<Foo, Bar>()
        .WithLogging()
        .IgnoringMember(dest => dest.DestOnlyProperty)
        .WhereMember(dest => dest.StatusCode)
            .ShouldEqual(src => src.Status)
        .WhereMember(dest => dest.IsValid).ShouldEqualValue(true)
        .WhereMember(dest => dest.Percent)
            .IsTestedBy((src, dest) => 
                Assert.AreEqual(src.Rate / 100, dest.Percent))
        .AssertMappedValues(foo, bar);

You don’t have to configure anything for properties with the same name/type in the source and destination instances. AssertMappedValues() considers those successful if the source/destination values match.

Use IgnoringMember for destination properties that are not mapped, or which you need to test in another way.

Use WhereMember to “dot” to the ShouldEqual, ShouldEqualValue and IsTestedBy functions:

MapMemberTester<TSource, TDestination>

class SparkyTestHelpers.Mapping.MapMemberTester<TSource, TDestination>

This class is for testing that a property was successfully “mapped” from one type to another.

Methods

• MapTester<TSource, TDestination> ShouldEqual(Expression<Func<TSource, Object>> sourceExpression)
  use to verify destination property mapped from differently named source property(s)
• MapTester<TSource, TDestination> ShouldEqualValue(Object value)
  use to verify destination property using a constant or some other value not derived from the source
• MapTester<TSource, TDestination> IsTestedBy(Action<TSource, TDestination> customTest)
  use for custom complex validation that doesn’t fit one of the other verification methods

RandomValuesHelper

class SparkyTestHelpers.Mapping.RandomValuesHelper

Test helper for updating class instance properties with random values (so you can fill a “source” instance without writing a lot of code).

Methods

• T CreateInstanceWithRandomValues()
• T UpdatePropertiesWithRandomValues(T instance)

Example

using SparkyTestHelpers.Mapping;
Foo foo = 
    new RandomValuesHelper()
        .CreateInstanceWithRandomValues<Foo>();
    var bar = new Bar();
    new RandomValuesHelper().UpdatePropertiesWithRandomValues(bar);

SparkyTestHelpers.AutoMapper

Extension Methods specifically for AutoMapper

• TDestination AssertAutoMappedValues(TSource source)
  calls Mapper.Map<TSource, TDestination>(source), then AssertMappedValues()
• TDestination AssertAutoMappedRandomValues()
  uses RandomValuesHelper to create a new TSource instance, calls Mapper.Map<TSource, TDestination>(source), then AssertMappedValues()

Examples:

Create a test source instance, then call AssertAutoMappedValues to:

• Use AutoMapper to map to a destination type instance
• AssertMappedValues

using SparkyTestHelpers.AutoMapper;
...
Baz baz = CreateAndPopulateTestBax();
Qux qux = MapTester.ForMap<Baz, Qux>.AssertAutoMappedValues(baz);

…or even better — with a single line of code:

• Create a test source instance with randomly generated values
• Use AutoMapper to map to a destination type instance
• AssertMappedValues

using SparkyTestHelpers.AutoMapper;
...
MapTester.ForMap<Baz, Qux>.AssertAutoMappedRandomValues();

Happy Testing!