add tests

tests/valid/src/for_stmt.ri

@@ -14,6 +14,14 @@ test "`for` statement with dynamic array" {
     @assert(sum == 55);
 }
 
+test "`for` statement with slice" {
+    mut sum := 0;
+    for i in [1, 2, 3, 4, 5, 6, 7, 8, 9, 10][:] {
+        sum += i;
+    }
+    @assert(sum == 55);
+}
+
 test "`for` statement with `string.as_bytes()`" {
     mut sum := 0;
     for b in "Hello World!".as_bytes() {

tests/valid/src/slices.ri

@@ -0,0 +1,17 @@
+test "creating slices from arrays" {
+    arr := [1, 2, 3, 4];
+    slice := arr[:];
+    @assert(slice[0] == 1);
+    @assert(slice[1] == 2);
+    @assert(slice[2] == 3);
+    @assert(slice[3] == 4);
+}
+
+test "creating slices from dynamic arrays" {
+    arr := +[1, 2, 3, 4];
+    slice := arr[:];
+    @assert(slice[0] == 1);
+    @assert(slice[1] == 2);
+    @assert(slice[2] == 3);
+    @assert(slice[3] == 4);
+}