.NET Datafixtures for Unit Tests
Test fixtures can be used to setup a certain environment state - usually a database. They make unit testing easier because you can easily enforce a particular state neccessary to test your code. Fixtures should be able to depend on each other, so that each fixture can focus on its own data.
This library provides a Fixture base class and a fixture loader that takes care of dependencies.
A simple fixture extends Fixture<T> and overrides DoLoad():
class StartOfUnixTime : Fixture<DateTime>
{
protected override DateTime DoLoad()
{
return new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
}
}To use this fixture, you need to load it:
var loader = new FixtureLoader();
var unixStart = loader.Add<StartOfUnixTime>();
loader.Load();
// The data generated by the fixture is available via the property "Result".
Assert.AreEqual(1970, unixStart.Result.Year);To make a fixture depend on another fixture, simply reference it as a constructor argument.
class UnixStartMessage : Fixture<string>
{
private readonly StartOfUnixTime start;
public UnixStartMessage(StartOfUnixTime start)
{
this.start = start;
}
protected override string DoLoad()
{
// You can access the result of the StartOfUnixTime
// fixture via its Result property
return "hello world, it is " + start.Result.Year;
}
}When loading this fixture, the dependant fixtures are loaded automatically. You just need to load the fixture you are actually using.
var loader = new FixtureLoader();
var msg = loader.Add<UnixStartMessage>();
loader.Load();
Assert.AreEqual("hello world, it is 1970", msg.Result);In a fixture, you probably want to add an entity to your db context and save the changes. The db context is just another dependency and can simply be injected as a constructor argument.
class FirstStudent : Fixture<Student>
{
private readonly SchoolDbContext schoolDb;
public UnixStartMessage(SchoolDbContext schoolDb)
{
this.schoolDb = schoolDb;
}
protected override Student DoLoad()
{
var first = new Student()
{
StudentName = "Donald Knuth"
};
schoolDb.Students.AddObject( first );
return first;
}
}Loading Database fixtures has a few implications. If you want your database to be in a repeatable state, you have to empty it first. You can use the utility class EntityFixtures to drop the entire database, initialize it, and load your fixtures:
var schoolDb = new SchoolDbContext();
FixtureLoader loader = EntityFixtures.DropCreateDatabase(scoolDb)
var first = loader.add<FirstStudent>();
loader.load();
// now you have a clean database with the first student
System.Diagnostics.Trace.WriteLine("First student: " + first.Result.StudentName); // => "First student: Donald Knuth"You should use a LocalDB for your unittests. EntityFixtures.DropCreateDatabase() actually throws an exception if you do not, but in any case: use your own brain.
If you have a look at EntityFixtures.DropCreateDatabase(), it just calls FixtureLoader.RegisterService() with your DbContext, and thereby making it available for constructor injection:
loader.RegisterService<TContext>(context);You are of course free to register and use other dependencies.
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