*** Test 1 - add ***
size=9: a, b, c, f, i, j, m, r, z

*** Test 2 - contains ***
size=7: a, c, j, l, n, p, y
contains('a')=true
contains('x')=false
contains('p')=true

*** Test 3 - remove leaf ***
size=8: b, d, f, g, l, m, n, z
contains('g')=true
remove('g')=true
size=7: b, d, f, l, m, n, z
contains('g')=false
remove('g')=false

*** Test 4 - remove inner node ***
size=8: b, d, f, g, l, m, n, z
contains('d')=true
remove('d')=true
size=7: b, f, g, l, m, n, z
contains('d')=false

*** Test 5 - remove root ***
size=8: b, d, f, g, l, m, n, z
contains('l')=true
remove('l')=true
size=7: b, d, f, g, m, n, z
contains('l')=false

*** Test 6 - union, intersect, diff ***
set1= size=3: a, b, c
set2= size=3: c, d, e
set1.union(set2)= size=5: a, b, c, d, e
set1.intersect(set2)= size=1: c
set1.diff(set2)= size=2: a, b
set2.diff(set1)= size=2: d, e

*** Test 7 - insert sorted values ***
size=26: a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, z

*** Test 8 - illegal arguments ***
add('1'): java.lang.IllegalArgumentException
contains('1'): java.lang.IllegalArgumentException
remove('1'): java.lang.IllegalArgumentException