add a test case

Makefile

@@ -12,3 +12,7 @@ all: true false
 
 %.o: %.s
 	$(AS) -o $@ $<
+
+.PHONY: test
+test:
+	@BIN=. test/true.sh

test/true.sh

@@ -0,0 +1,29 @@
+#!/bin/bash
+set -eu
+set -o pipefail
+
+: ${BIN:-..}
+: ${EMU:=qemu-riscv64}
+
+cmd=$BIN/true
+name=true
+
+fail=0
+err() {
+    echo "FAIL $name: $*"
+    fail=1
+}
+
+out=$($EMU $cmd)
+stat=$?
+if [ -n "$out" ]; then
+    err "expected no output"
+fi
+
+if [ "$stat" -ne 0 ]; then
+    err "exited with status code $stat, expected 0"
+fi
+
+if [ "$fail" -eq 0 ]; then
+    echo PASS $name
+fi