public void TestMissingInteger()
{
int[] A = new int[] { 1, 3, 6, 4, 1, 2 };
int expected = 5;
int actual = Lessons.MissingInteger(A);
Assert.AreEqual(expected, actual);
A = new int[] { 1, 2, 3 };
expected = 4;
actual = Lessons.MissingInteger(A);
Assert.AreEqual(expected, actual);
A = new int[] { -1, -3 };
expected = 1;
actual = Lessons.MissingInteger(A);
Assert.AreEqual(expected, actual);
A = new int[] { 2 };
expected = 1;
actual = Lessons.MissingInteger(A);
Assert.AreEqual(expected, actual);
}