diff --git a/builtin/string_test.v b/builtin/string_test.v
new file mode 100644
index 0000000000..b88867befa
--- /dev/null
+++ b/builtin/string_test.v
@@ -0,0 +1,246 @@
+fn test_add() {
+	mut a := 'a'
+	a += 'b'
+	assert a.eq('ab')
+	a = 'a'
+	for i := 1; i < 1000; i++ {
+		a += 'b'
+	}
+	assert a.len == 1000
+	assert a.ends_with('bbbbb')
+	a += '123'
+	assert a.ends_with('3')
+}
+
+fn test_ends_with() {
+	a := 'browser.v'
+	assert a.ends_with('.v')
+}
+
+fn test_between() {
+	 s := 'hello [man] how you doing'
+	assert s.find_between('[', ']') == 'man'
+}
+
+fn test_compare() {
+	a := 'Music'
+	b := 'src'
+	assert b.ge(a)
+}
+
+fn test_sort() {
+	mut vals := [
+	'src', 'Music', 'go'
+	]
+	len := vals.len
+	vals.sort()
+	assert len == vals.len
+	assert vals[0] == 'Music'
+	assert vals[1] == 'go'
+	assert vals[2] == 'src'
+}
+
+fn test_split() {
+	mut s := 'volt/twitch.v:34'
+	mut vals := s.split(':')
+	assert vals.len == 2
+	assert vals[0]== 'volt/twitch.v'
+	assert vals[1]== '34'
+	// /////////
+	s = '2018-01-01z13:01:02'
+	vals = s.split('z')
+	assert vals.len == 2
+	assert vals[0]=='2018-01-01'
+	assert vals[1]== '13:01:02'
+	// /////////////
+	s = '4627a862c3dec29fb3182a06b8965e0025759e18___1530207969___blue'
+	vals = s.split('___')
+	assert vals.len == 3
+	assert vals[0]== '4627a862c3dec29fb3182a06b8965e0025759e18'
+	assert vals[1]=='1530207969'
+	assert vals[2]== 'blue'
+}
+
+fn test_trim_space() {
+	a := ' a '
+	assert a.trim_space() == 'a'
+	code := '
+
+fn main() {
+        println(2)
+}
+
+'
+	code_clean := 'fn main() {
+        println(2)
+}'
+	assert code.trim_space() == code_clean
+}
+
+fn test_join() {
+	mut strings := [ 'a', 'b', 'c' ]
+	mut s := strings.join(' ')
+	assert s == 'a b c'
+	strings = ['one
+two ',
+	'three! 
+four!']
+	s = strings.join(' ')
+	assert s.contains('one') && s.contains('two ') && s.contains('four')
+}
+
+fn test_clone() {
+	mut a := 'a'
+	a += 'a'
+	a += 'a'
+	mut b := a
+	mut c := a.clone()
+	assert c == a
+	assert c == 'aaa'
+	assert b == 'aaa'
+}
+
+fn test_replace() {
+	a := 'hello man!'
+	mut b := a.replace('man', 'world')
+	assert b.eq('hello world!')
+	b = b.replace('!', '')
+	assert b.eq('hello world')
+	b = b.replace('h', 'H')
+	assert b.eq('Hello world')
+	b = b.replace('kek', 'lul')
+	assert b.eq('Hello world')
+	s := 'hey man how are you'
+	assert s.replace('man ', '') == 'hey how are you'
+	lol := 'lol lol lol'
+	assert lol.replace('lol', 'kek') == 'kek kek kek'
+	b = 'oneBtwoBBthree'
+	assert b.replace('B', '') == 'onetwothree'
+	b = '**char'
+	assert b.replace('*char', 'byteptr') == '*byteptr'
+}
+
+fn test_itoa() {
+	num := 777
+	assert num.str() == '777'
+	big := 7779998
+	assert big.str() == '7779998'
+	a := 3
+	assert a.str() == '3'
+	b := 5555
+	assert b.str() == '5555'
+	zero := 0
+	assert zero.str() == '0'
+	neg := -7
+	assert neg.str() == '-7'
+}
+
+fn test_reassign() {
+	a := 'hi'
+	mut b := a
+	b += '!'
+	assert a == 'hi'
+	assert b == 'hi!'
+}
+
+fn test_runes() {
+	s := 'привет'
+	assert s.len == 12
+	s2 := 'privet'
+	assert s2.len == 6
+	u := s.ustring()
+	assert u.len == 6
+	assert s2.substr(1, 4).len == 3
+	assert s2.substr(1, 4) == 'riv'
+	assert u.substr(1, 4).len == 6
+	assert u.substr(1, 4) == 'рив'
+	assert s2.substr(1, 2) == 'r'
+	assert u.substr(1, 2) == 'р'
+	assert s2.ustring().at(1) == 'r'
+	assert u.at(1) == 'р'
+	// ///////
+	first := u.at(0)
+	last := u.at(u.len - 1)
+	assert first.len == 2
+	assert last.len == 2
+}
+
+fn test_lower() {
+	mut s := 'A'
+	assert s.to_lower() == 'a'
+	assert s.to_lower().len == 1
+	s = 'HELLO'
+	assert s.to_lower() == 'hello'
+	assert s.to_lower().len == 5
+	s = 'Aloha'
+	assert s.to_lower() == 'aloha'
+	s = 'Have A nice Day!'
+	assert s.to_lower() == 'have a nice day!'
+	s = 'hi'
+	assert s.to_lower() == 'hi'
+}
+
+fn test_left_right() {
+	s := 'ALOHA'
+	assert s.left(3) == 'ALO'
+	assert s.right(3) == 'HA'
+	u := s.ustring()
+	assert u.left(3) == 'ALO'
+	assert u.right(3) == 'HA'
+}
+
+fn test_contains() {
+	s := 'view.v'
+	assert s.contains('vi')
+	assert !s.contains('random')
+}
+
+fn test_arr_contains() {
+	a := ['a', 'b', 'c']
+	assert a.contains('b')
+	ints := [1, 2, 3]
+	assert ints.contains(2)
+}
+
+fn test_to_num() {
+	s := '7'
+	assert s.to_i() == 7
+	f := '71.5 hasdf'
+	assert f.to_float() == 71.5
+	b := 1.52345
+	mut a := '${b:.03f}'
+	assert a == '1.523'
+	num := 7
+	a = '${num:03d}'
+	vals := ['9']
+	assert vals[0].to_i() == 9
+}
+
+fn test_hash() {
+	s := '10000'
+	assert s.hash() == 46730161
+	s2 := '24640'
+	assert s2.hash() == 47778736
+	s3 := 'Content-Type'
+	assert s3.hash() == 949037134
+	s4 := 'bad_key'
+	assert s4.hash() == -346636507
+	s5 := '24640'
+	// From a map collision test
+	assert s5.hash() % ((1 << 20) -1) == s.hash() % ((1 << 20) -1)
+	assert s5.hash() % ((1 << 20) -1) == 592861
+}
+
+fn test_trim_left() {
+	mut s := 'module main'
+	assert s.trim_left(' ') == 'module main'
+	s = ' module main'
+	assert s.trim_left(' ') == 'module main'
+}
+
+fn test_all_after() {
+	s := 'fn hello'
+	q := s.all_after('fn ')
+	assert q == 'hello'
+}
+