arrays: improve `range` function

vlib/arrays/arrays.v

@@ -1,10 +1,9 @@
 module arrays
 
-fn range<T>(start, end T) []T {
-	mut res := [start]
-	for i := start + 1; i < end; i++ {
+pub fn range<T>(start, end T) []T {
+	mut res := []T
+	for i := start; i < end; i++ {
 		res << i
 	}
 	return res
 }
-

vlib/arrays/arrays_test.v

@@ -1,10 +1,28 @@
 import arrays
 
 fn test_range() {
-	/*
-	TODO
-	a := arrays.range(1, 10)
-	assert a[0] == 1
-	println(a)
-	*/
+	start_pos := 3
+	end_pos := 10
+
+	arr1 := arrays.range<int>(start_pos, end_pos)
+	assert arr1.len == end_pos - start_pos
+	for i, c in arr1 {
+		assert c == i + start_pos
+	}
+
+	arr2 := arrays.range<f32>(start_pos, end_pos)
+	assert arr2.len == end_pos - start_pos
+	for i, c in arr2 {
+		assert c == f32(i + start_pos)
+	}
+
+	arr3 := arrays.range<int>(start_pos, start_pos - 1)
+	assert arr3.len == 0
+
+	arr4 := arrays.range<int>(start_pos, start_pos)
+	assert arr4.len == 0
+
+	arr5 := arrays.range<int>(start_pos, start_pos + 1)
+	assert arr5.len == 1
+	assert arr5[0] == start_pos
 }