Test.assertEquals(highAndLow("-1 -1 0"), "0 -1"); // First failure.
Oh ok. I made wrong conclusion by error message.

When sample test passes nicely, got this at actual test:
Failed asserting that two strings are equal
Expected: '0 -1'
Actual : '-1 -1'
After rearranging code got this at sample test:
Failed asserting that two strings are equal
Expected: '1 1'
Actual : '0 1'
Why it changes the rules how to represent results with equal min and max?