test architecture

SequentialProviderTest.cs

namespace ThickClient.SequentialNumber.Tests
{
...
    [TestClass]
    public class SequentialProviderTest
    {
        [TestMethod]
        public void CreatsEmptyFile()
        {
            // Arrange
            Mock<IFileSystem> mock = new Mock<IFileSystem>(MockBehavior.Strict);
            mock.Setup(x => x.ReadAllText(_filePath)).Throws<FileNotFoundException>();

            // Act
            SequentialProviderMock sequentialProvider = new SequentialProviderMock(mock.Object);

            // Assert
            sequentialProvider.GetCurrent().Root.HasElements.Should().BeFalse();
            mock.VerifyAll();
        }
        ...
                [TestMethod]
        public void NextingEmpty()
        {
            // Arrange
            Mock<IFileSystem> mock = new Mock<IFileSystem>(MockBehavior.Strict);
            mock.Setup(x => x.ReadAllText(_filePath)).Throws<FileNotFoundException>();
            mock.Setup(x => x.WriteAllText(_filePath, It.IsAny<string>()));
            SequentialProviderMock sequentialProvider = new SequentialProviderMock(mock.Object);

            // Act
            decimal result = sequentialProvider.NextTicket();

            // Assert
            result.ShouldBeEquivalentTo(-1M);
            XElement root = sequentialProvider.GetCurrent().Root;
            root.Should().HaveElement(SequentialProvider.NodeNamesForLevel[0]);
            XElement first = (XElement)root.FirstNode;
            first.Should().HaveAttribute("sequenceNumber", "-1");
            mock.VerifyAll();
        }

...