public void IsValid_GivenCollectionWithWithoutAllCellsWithValues1to9_ReturnFalse()
{
var sut = new CellCollection("");
sut.Cells.Add(TestUtilities.CreateCell(1));
sut.Cells.Add(TestUtilities.CreateCell(2));
sut.Cells.Add(TestUtilities.CreateCell(3));
sut.Cells.Add(TestUtilities.CreateCell(4));
sut.Cells.Add(TestUtilities.CreateCell(6));
sut.Cells.Add(TestUtilities.CreateCell(7));
sut.Cells.Add(TestUtilities.CreateCell(9));
var result = sut.IsValid();
Assert.IsFalse(result);
}