Look for $a0 as argument of exit syscall.

tests/syntax/asciiz-wrong-param.s

@@ -4,6 +4,7 @@ msg:
 
 	.text
 main:
+	li	$a0, 0
 	li	$v0, 10
 	syscall
 	
\ No newline at end of file

tests/syntax/too-many-operands.s

 	.text
 main:
 	add	$t0, $t1, $t2, $t3, $t4
+	li	$a0, 0
 	li	$v0, 10
 	syscall

tests/unlimited/simple-exp.s

@@ -22,6 +22,7 @@ main:
 	li	$v0, 4
 	syscall
 	
+	li	$a0, 0
 	li	$v0, 10
 	syscall
 	
\ No newline at end of file