Unit tests code for a Java class that that checks whether an array is sorted
I don't see anything wrong with the way you are testing.

You may want to include negative numbers in your test cases. 

I prefer to have test cases broken up. It's easier to track down failing tests:

@Test
public void testIsSortedSingleNode()
{
    int[] C = { 32 };
    assertEquals(true, SortedOrNot.isSorted(C));
}


Even in tests you should follow naming standards. Names such as A, B C are not very descriptive. Also they should start with a lower-case letter. result would be a better name. You use the same variable throughout.

Use assertTrue and assertFalse instead of assertEquals(true/false, x).

IMO arrayLength would be a better name then n. Or you could use arr.length.