/// <summary>
/// Compiles the <paramref name="syntaxTree" />, instantiates all non-abstract classes implementing
/// <see cref="ITestableObject" />, and returns them.
/// </summary>
/// <param name="syntaxTree">The syntax tree that should be compiled.</param>
protected IEnumerable<ITestableObject> GetTestableObjects(SyntaxTree syntaxTree)
{
var compilation = CreateCompilation(syntaxTree);
var semanticModel = compilation.GetSemanticModel(syntaxTree);
var testableTypes = syntaxTree
.Descendants<ClassDeclarationSyntax>()
.Select(declaration => declaration.GetTypeSymbol(semanticModel))
.Where(symbol => !symbol.IsGenericType && !symbol.IsAbstract && symbol.ContainingType == null)
.Where(symbol => symbol.IsDerivedFrom(semanticModel.GetTypeSymbol<ITestableObject>()))
.Select(symbol => symbol.ToDisplayString())
.ToArray();
if (testableTypes.Length == 0)
throw new TestException("Unable to find any testable class declarations.");
var assembly = CompileSafetySharp(compilation);
return testableTypes.Select(testableType => (ITestableObject)Activator.CreateInstance(assembly.GetType(testableType)));
}