https://en.wikipedia.org/wiki/Plan_9_from_Bell_Labs since the author seems to be confused in this regard.
assertException(() => upcase(12));
assertException(() => upcase(true));
assertException(() => upcase(null));
assertException(() => upcase(new Object()));
...
assertEquals("TEST", upcase("test"));
assertEquals("HELLO, WORLD", upcase("hElLo, wOrLd"));
assertEquals("BLA123", upcase("bla123"));