Intro to context classes

Context classes allow you to create encapsulated behaviors that can be consumed in a spec. You can easily reuse context across test fixtures in a variety of ways. There's the typical inheritance-based approach:

C#

public class OrderProcessorSpecs
{
	public class when_processing_an_order : given.the_item_is_available
	{
		private OrderResult _result;

		protected override void When()
		{
			_result = SUT.Process(new Order { PartNumber = "TestPart", Quantity = 10 });
		}

		[Test]
		public void then_the_order_is_accepted()
		{
			_result.WasAccepted.ShouldBeTrue();	
		}

		[Test]
		public void then_it_checks_the_inventory()
		{
			GetMockFor<IInventory>().Verify();
		}

		[Test]
		public void then_it_raises_an_order_submitted_event()
		{
			GetMockFor<IPublisher>()
				.Verify(p => p.Publish(It.Is<OrderSubmitted>(o => o.OrderNumber == _result.OrderNumber)));
		}
	}

	
	public class when_processing_an_order_with_a_negative_quantity : given.the_item_is_available
	{
		private OrderResult _result;

		protected override void When()
		{
			_result = SUT.Process(new Order{ PartNumber = "TestPart", Quantity = -1});
		}

		[Test]
		public void then_the_order_is_rejected()
		{
			_result.WasAccepted.ShouldBeFalse();
		}

		[Test]
		public void then_it_does_not_check_the_inventory()
		{
			GetMockFor<IInventory>()
				.Verify(i => i.IsQuantityAvailable("TestPart", -1), Times.Never());
		}

		[Test]
		public void then_it_does_not_raise_an_order_submitted_event()
		{
			GetMockFor<IPublisher>()
				.Verify(p => p.Publish(It.IsAny<OrderSubmitted>()), Times.Never());
		}
	}

	public class given
	{
		public class the_item_is_available : SpecsFor<OrderProcessor>
		{
			protected override void Given()
			{
				GetMockFor<IInventory>()
					.Setup(i => i.IsQuantityAvailable("TestPart", 10))
					.Returns(true)
					.Verifiable();
			}
		}
	}
}