Add some posix error tests
diff --git a/tests/posix_errors.txt b/tests/posix_errors.txt
index e13205c..4600a94 100644
--- a/tests/posix_errors.txt
+++ b/tests/posix_errors.txt
@@ -5,7 +5,9 @@
 read()
 print "i: ", i
 halt
-return 0
+define x(e) { return 0; }
+define x(e) { return 4*(e+e); }
+define x(e) { return (e+e)*4; }
 limits
 .
 a(a[])