Creating a Simple Item

The code below creates a fake in-memory database with a single item Home that contains the Title field with the 'Welcome!' value (the xUnit unit testing framework is used):

[Fact]
public void HowToCreateSimpleItem()
{
  using (Sitecore.FakeDb.Db db = new Sitecore.FakeDb.Db
    {
      new Sitecore.FakeDb.DbItem("Home") { { "Title", "Welcome!" } }
    })
  {
    Sitecore.Data.Items.Item home = db.GetItem("/sitecore/content/home");
    Xunit.Assert.Equal("Welcome!", home["Title"]);
  }
}

Important:

You should always dispose the 'db' instance properly. By default Sitecore databases are singletons, so ignoring proper test data cleaning may lead to unstable behavior in tests.