@Test
	public void testNestedMarkReleasedTwice() {
		CharStream input = createStream("");
		int m1 = input.mark();
		int m2 = input.mark();
		input.release(m2);
		assertThrows(IllegalStateException.class, () -> input.release(m2));
	}
The {@link IntStream} interface does not specify the behavior when a mark
is released twice, but {@link UnbufferedCharStream} handles this case by
throwing an {@link IllegalStateException}.
tool-testsuite/test/org/antlr/v4/test/tool/TestUnbufferedCharStream.java