diff --git a/vlib/builtin/map_test.v b/vlib/builtin/map_test.v
index 1d426046f0..f88b58c07e 100644
--- a/vlib/builtin/map_test.v
+++ b/vlib/builtin/map_test.v
@@ -1,4 +1,67 @@
-// import time
+import rand
+
+const (
+	strings = unique_strings(20000, 10)
+)
+
+fn unique_strings(arr_len int, str_len int) []string {
+	mut arr := []string{}
+	for arr.len < arr_len {
+		str := rand.string(str_len)
+		if str !in arr {
+			arr << str
+		}
+	}
+	return arr
+}
+
+fn test_get_and_set_many() {
+	mut m := map[string]int{}
+	for i, s in strings {
+		m[s] = i
+		assert m[s] == i
+		assert m.len == i + 1
+	}
+	for i, s in strings {
+		assert m[s] == i
+	}
+	assert m.len == strings.len
+}
+
+fn test_for_in_many() {
+	mut m := map[string]int{}
+	for i, s in strings {
+		m[s] = i
+	}
+	for k, v in m {
+		assert m[k] == v
+	}
+}
+
+fn test_keys_many() {
+	mut m := map[string]int{}
+	for i, s in strings {
+		m[s] = i
+	}
+	keys := m.keys()
+	assert keys.len == strings.len
+	assert keys.len == m.len
+	assert keys == strings
+}
+
+fn test_deletes_many() {
+	mut m := map[string]int{}
+	for i, s in strings {
+		m[s] = i
+	}
+	for i, s in strings {
+		m.delete(s)
+		assert m[s] == 0
+		assert m.len == strings.len - (i + 1)
+	}
+	assert m.len == 0
+	assert m.keys().len == 0
+}
 
 struct User {
 mut:
@@ -7,7 +70,7 @@ mut:
 
 struct Aaa {
 mut:
-	m map[string]int
+	m     map[string]int
 	users map[string]User
 }
 
@@ -16,7 +79,7 @@ fn (mut a Aaa) set(key string, val int) {
 }
 
 fn test_map() {
-	mut m := map[string]int
+	mut m := map[string]int{}
 	assert m.len == 0
 	m['hi'] = 80
 	m['hello'] = 101
@@ -39,18 +102,17 @@ fn test_map() {
 	assert m.len == 1
 	m.delete('aloha')
 	assert m.len == 1
-
 	assert m['hi'] == 0
 	assert m.keys().len == 1
 	assert m.keys()[0] == 'hello'
-	////
-	mut users := map[string]User
+	// //
+	mut users := map[string]User{}
 	users['1'] = User{'Peter'}
 	peter := users['1']
-	assert  peter.name == 'Peter'
+	assert peter.name == 'Peter'
 	mut a := Aaa{
-		m: map[string]int
-		users: map[string]User
+		m: map[string]int{}
+		users: map[string]User{}
 	}
 	a.users['Bob'] = User{'Bob'}
 	q := a.users['Bob']
@@ -66,99 +128,86 @@ fn test_map() {
 }
 
 fn test_map_init() {
-	m := { 'one': 1, 'two': 2 }
+	m := {
+		'one': 1
+		'two': 2
+	}
 	assert m['one'] == 1
 	assert m['two'] == 2
 	assert m['three'] == 0
 }
 
 fn test_string_map() {
-	//m := map[string]Fn
+	// m := map[string]Fn
 }
 
 fn test_large_map() {
-	//ticks := time.ticks()
-	mut nums := map[string]int
+	// ticks := time.ticks()
+	mut nums := map[string]int{}
 	n := 30 * 1000
-	for i in 0..n {
-	        key := i.str()
-	        nums[key] = i
+	for i in 0 .. n {
+		key := i.str()
+		nums[key] = i
 	}
 	assert nums['1'] == 1
 	assert nums['999'] == 999
 	assert nums['1000000'] == 0
-	//println(time.ticks() - ticks)
+	// println(time.ticks() - ticks)
 }
 
 fn test_various_map_value() {
-	mut m1 := map[string]int
+	mut m1 := map[string]int{}
 	m1['test'] = 1
 	assert m1['test'] == 1
-
-	mut m2 := map[string]string
+	mut m2 := map[string]string{}
 	m2['test'] = 'test'
 	assert m2['test'] == 'test'
-
-	mut m3 := map[string]i8
+	mut m3 := map[string]i8{}
 	m3['test'] = i8(0)
 	assert m3['test'] == i8(0)
-
-	mut m4 := map[string]i16
+	mut m4 := map[string]i16{}
 	m4['test'] = i16(0)
 	assert m4['test'] == i16(0)
-
-	mut m7 := map[string]u16
+	mut m7 := map[string]u16{}
 	m7['test'] = u16(0)
 	assert m7['test'] == u16(0)
-
-	mut m8 := map[string]u32
+	mut m8 := map[string]u32{}
 	m8['test'] = u32(0)
 	assert m8['test'] == u32(0)
-
-	mut m9 := map[string]bool
+	mut m9 := map[string]bool{}
 	m9['test'] = true
 	assert m9['test'] == true
-
-	mut m10 := map[string]byte
+	mut m10 := map[string]byte{}
 	m10['test'] = byte(0)
 	assert m10['test'] == byte(0)
-
-	mut m11 := map[string]f32
+	mut m11 := map[string]f32{}
 	m11['test'] = f32(0.0)
 	assert m11['test'] == f32(0.0)
-
-	mut m12 := map[string]f64
+	mut m12 := map[string]f64{}
 	m12['test'] = f64(0.0)
 	assert m12['test'] == f64(0.0)
-
-	//mut m13 := map[string]rune
-	//m13['test'] = rune(0)
-	//assert m13['test'] == rune(0)
-
-	mut m14 := map[string]voidptr
+	// mut m13 := map[string]rune
+	// m13['test'] = rune(0)
+	// assert m13['test'] == rune(0)
+	mut m14 := map[string]voidptr{}
 	m14['test'] = voidptr(0)
 	assert m14['test'] == voidptr(0)
-
-	mut m15 := map[string]byteptr
+	mut m15 := map[string]byteptr{}
 	m15['test'] = byteptr(0)
 	assert m15['test'] == byteptr(0)
-
-	mut m16 := map[string]i64
+	mut m16 := map[string]i64{}
 	m16['test'] = i64(0)
 	assert m16['test'] == i64(0)
-
-	mut m17 := map[string]u64
+	mut m17 := map[string]u64{}
 	m17['test'] = u64(0)
 	assert m17['test'] == u64(0)
-
-	mut m18 := map[string]&int
+	mut m18 := map[string]&int{}
 	m18['test'] = &int(0)
 	assert m18['test'] == &int(0)
 }
 
-
 fn test_string_arr() {
-	mut m := map[string][]string
+	mut m := map[string][]string{}
 	m['a'] = ['one', 'two']
 	assert m['a'].len == 2
 	assert m['a'][0] == 'one'
@@ -170,14 +219,14 @@ fn mut_map(mut m map[string]int) {
 }
 
 fn test_mut_arg() {
-	mut m := map[string]int
+	mut m := map[string]int{}
 	mut_map(mut m)
 	a := m['a']
 	assert a == 10
 }
 
 fn test_delete() {
-	mut m := map[string]int
+	mut m := map[string]int{}
 	m['one'] = 1
 	m['two'] = 2
 	println(m['two']) // => "2"
@@ -188,18 +237,18 @@ fn test_delete() {
 }
 
 fn test_delete_size() {
-    arr := ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9']
-    mut m := map[string]int
-    for _ in 0..10 {
-        for i in 0..10 {
-            m[arr[i]] = i
-        }
-        assert(m.len == 10)
-        println(m.len)
-        for i in 0..10 {
-            m.delete(arr[i])
-        }
-    }
+	arr := ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9']
+	mut m := map[string]int{}
+	for _ in 0 .. 10 {
+		for i in 0 .. 10 {
+			m[arr[i]] = i
+		}
+		assert (m.len == 10)
+		println(m.len)
+		for i in 0 .. 10 {
+			m.delete(arr[i])
+		}
+	}
 }
 
 struct Mstruct1 {
@@ -233,19 +282,20 @@ fn test_map_assign() {
 		's': u16(5)
 		't': 3
 	}
-	_ := Mstruct1 {
-		{ 'p': 12 }
-	}
-	_ := Mstruct2 {
-		{ 'q': 1.7 }
-	}
-	_ := Mstruct3 {
-		{ 'r': u16(6), 's': 5 }
-	}
+	_ := Mstruct1{{
+		'p': 12
+	}}
+	_ := Mstruct2{{
+		'q': 1.7
+	}}
+	_ := Mstruct3{{
+		'r': u16(6)
+		's': 5
+	}}
 }
 
 fn test_postfix_op_directly() {
-	mut a := map[string]int
+	mut a := map[string]int{}
 	a['aaa']++
 	assert a['aaa'] == 1
 	a['aaa']++
@@ -257,14 +307,14 @@ fn test_postfix_op_directly() {
 }
 
 fn test_map_push_directly() {
-	mut a := map[string][]string
+	mut a := map[string][]string{}
 	a['aaa'] << ['a', 'b', 'c']
 	assert a['aaa'].len == 3
 	assert a['aaa'] == ['a', 'b', 'c']
 }
 
 fn test_assign_directly() {
-	mut a := map[string]int
+	mut a := map[string]int{}
 	a['aaa'] += 4
 	assert a['aaa'] == 4
 	a['aaa'] -= 2
@@ -272,21 +322,28 @@ fn test_assign_directly() {
 }
 
 fn test_map_in_directly() {
-	for k, v in {'aa': 1} {
+	for k, v in {
+		'aa': 1
+	} {
 		assert k == 'aa'
 		assert v == 1
 	}
 }
 
 fn test_plus_assign_string() {
-	mut m := {'one': ''}
+	mut m := {
+		'one': ''
+	}
 	m['one'] += '1'
 	assert m.len == 1
 	assert m['one'] == '1'
 }
 
 fn test_map_keys_to_array() {
-	m := {'a': 'b', 'c': 'd'}
+	m := {
+		'a': 'b'
+		'c': 'd'
+	}
 	mut arr := []string{}
 	for k, _ in m {
 		arr << k
@@ -303,7 +360,9 @@ fn map_in_mut(mut m map[string]int) {
 }
 
 fn test_map_in_mut() {
-	mut m := {'one': 1}
+	mut m := {
+		'one': 1
+	}
 	map_in_mut(mut m)
 	assert m['one'] == 2
 }
@@ -330,7 +389,10 @@ fn mut_map_with_relation_op_in_fn(mut m map[string]int) {
 }
 
 fn test_mut_map_with_relation_op_in_fn() {
-	mut m := {'one':1, 'two':2}
+	mut m := {
+		'one': 1
+		'two': 2
+	}
 	mut_map_with_relation_op_in_fn(mut m)
 	assert 'three' in m
 	assert 'four' in m
@@ -342,20 +404,23 @@ fn test_mut_map_with_relation_op_in_fn() {
 
 fn test_map_str_after_delete() {
 	mut m := {
-		'first': 1,
-		'second': 2,
-		'third': 3,
+		'first': 1
+		'second': 2
+		'third': 3
 	}
 	osm := '$m'
 	m.delete('second')
 	nsm := '$m'
-    println('m: $m')
+	println('m: $m')
 	assert osm == "{'first': 1, 'second': 2, 'third': 3}"
 	assert nsm == "{'first': 1, 'third': 3}"
 }
 
 fn test_modify_map_value() {
-	mut m1 := {'foo': 3, 'bar': -7}
+	mut m1 := {
+		'foo': 3
+		'bar': -7
+	}
 	m1['foo'] += 5
 	m1['bar'] *= -2
 	assert m1['foo'] == 8