/// <summary>
/// Check that the given function uses deferred execution.
/// A "spiked" source is given to the function: the function
/// call itself shouldn't throw an exception. However, using
/// the result (by calling GetEnumerator() then MoveNext() on it) *should*
/// throw InvalidOperationException.
/// </summary>
public static void AssertDeferred <T>(
Func <IEnumerable <int>, IEnumerable <T> > deferredFunction)
{
ThrowingEnumerable source = new ThrowingEnumerable();
var result = deferredFunction(source);
using (var iterator = result.GetEnumerator())
{
Assert.Throws <InvalidOperationException>(() => iterator.MoveNext());
}
}
public void ExecutionIsDeferred()
{
ThrowingEnumerable.AssertDeferred(src => src.Where(x => x > 0));
}
public void ExecutionIsDeferred()
{
ThrowingEnumerable.AssertDeferred(src => src.Select(x => x * 2));
}