Add tests for split_by_ascii_whitespace (#428)

tests/should_succeed/ascii_test.jou

@@ -1,4 +1,6 @@
 import "stdlib/ascii.jou"
+import "stdlib/io.jou"
+import "stdlib/mem.jou"
 import "stdlib/str.jou"
 
 def main() -> int:
@@ -35,9 +37,20 @@ def main() -> int:
     assert not is_ascii_whitespace('.')
     assert not is_ascii_whitespace('\0')
 
-    s: byte[100]
-    strcpy(s, "  hello world \r\n  \t ")
+    s: byte[100] = "  hello world \r\n  \t "
     trim_ascii_whitespace(s)
     assert strcmp(s, "hello world") == 0
 
+    s = "  hello world \r\n  \t "
+    words = split_by_ascii_whitespace(s)
+    # Output: hello
+    # Output: world
+    for w = words; *w != NULL; w++:
+        puts(*w)
+    # Output: hello
+    # Output: world
+    for i = 0; words[i] != NULL; i++:
+        puts(words[i])
+    free(words)
+
     return 0