public void FlipRequired()
{
// Arrange.
Initialize();
CreateT_D();
// Act.
Triangle outFlip;
var isRequiredBefore = Triangulation.FlipRequired(T, out outFlip);
Triangulation.Flip(T, T_D);
var isRequiredAfter = Triangulation.FlipRequired(T, out outFlip);
// Assert.
Assert.IsTrue(isRequiredBefore);
Assert.IsFalse(isRequiredAfter);
}