public void ApplyValidSingleStepSolutionTest()
        {
            var sudoku = (int[, ])_sudoku.Clone();

            sudoku[4, 7] = 0;

            var sudokuPuzzle = new SudokuPuzzle(sudoku);
            var strategyWhichFindsNothing      = new NakedTriple();
            var strategyWhichReducesCandidates = new BasicElimination();
            var strategyWhichFindsResult       = new HiddenSingle();

            sudokuPuzzle.ApplySingleStepSolution(strategyWhichFindsNothing.SolveSingleStep(sudokuPuzzle));
            Assert.That(sudokuPuzzle.Steps, Is.Empty);
            Assert.That(sudokuPuzzle.NumberOfSteps, Is.Zero);

            sudokuPuzzle.ApplySingleStepSolution(strategyWhichReducesCandidates.SolveSingleStep(sudokuPuzzle));
            Assert.That(sudokuPuzzle.Steps.Count, Is.EqualTo(1));
            Assert.That(sudokuPuzzle.NumberOfSteps, Is.EqualTo(1));
            Assert.That(sudokuPuzzle.Steps.Last().Strategy, Is.EqualTo(strategyWhichReducesCandidates.StrategyName));
            Assert.That(sudokuPuzzle.Steps.Last().SolutionDescription, Is.Not.Empty);

            sudokuPuzzle.ApplySingleStepSolution(strategyWhichFindsResult.SolveSingleStep(sudokuPuzzle));
            Assert.That(sudokuPuzzle.Steps.Count, Is.EqualTo(2));
            Assert.That(sudokuPuzzle.NumberOfSteps, Is.EqualTo(2));
            Assert.That(sudokuPuzzle.Steps.Last().Strategy, Is.EqualTo(strategyWhichFindsResult.StrategyName));
            Assert.That(sudokuPuzzle.Cells[4, 7].Value, Is.EqualTo(5));
            Assert.That(sudokuPuzzle.Steps.Last().SolutionDescription, Is.Not.Empty);
        }
        public void UndoSingleStepSolutionsWhichReturnsEliminations_UndoesEliminations_Test()
        {
            var sudoku = (int[, ])_sudoku.Clone();

            sudoku[4, 7] = 0;

            var sudokuPuzzle = new SudokuPuzzle(sudoku);
            var strategyWhichReducesCandidates = new BasicElimination();

            sudokuPuzzle.ApplySingleStepSolution(strategyWhichReducesCandidates.SolveSingleStep(sudokuPuzzle));
            Assert.That(sudokuPuzzle.Cells[4, 7].CanBe.Single(), Is.EqualTo(5));

            var step = sudokuPuzzle.UndoLastSingleStepSolution();

            Assert.That(step.Eliminations, Is.Not.Empty);
            Assert.That(step.Result, Is.Null);
            Assert.That(step.Strategy, Is.EqualTo(strategyWhichReducesCandidates.StrategyName));
            Assert.That(step.SolutionDescription, Is.Not.Empty);
            CollectionAssert.AreEqual(sudokuPuzzle.Cells[4, 7].CanBe, new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 });
        }