assertEquals("zABCDEF", seq.getSequenceAsString());
seq.insertCharAt(2, 2, 'x');
assertEquals("zAxxBCDEF", seq.getSequenceAsString());
assertEquals("zABCDEF", seq.getSequenceAsString());
seq.insertCharAt(2, 2, 'x');
assertEquals("zAxxBCDEF", seq.getSequenceAsString());