Add smoke test for calibre

tests/test.sh

@@ -0,0 +1,37 @@
+#!/bin/bash
+set -euo pipefail
+
+IMAGE="$1"
+FAILED=0
+PASSED=0
+
+assert_eq() {
+  local desc="$1" expected="$2" actual="$3"
+  if [ "$expected" = "$actual" ]; then
+    echo "PASS: $desc"
+    PASSED=$((PASSED + 1))
+  else
+    echo "FAIL: $desc (expected $expected, got $actual)"
+    FAILED=$((FAILED + 1))
+  fi
+}
+
+TMPDIR="$(mktemp -d)"
+trap 'rm -rf "$TMPDIR"' EXIT
+
+docker run --rm "$IMAGE" calibre --version > "$TMPDIR/output" 2>&1 && RC=0 || RC=$?
+assert_eq "calibre --version exits cleanly" "0" "$RC"
+
+if [ -s "$TMPDIR/output" ]; then
+  echo "PASS: calibre --version produces output"
+  PASSED=$((PASSED + 1))
+else
+  echo "FAIL: calibre --version produces no output"
+  FAILED=$((FAILED + 1))
+fi
+
+echo ""
+echo "$PASSED/$((PASSED + FAILED)) tests passed"
+if [ "$FAILED" -gt 0 ]; then
+  exit 1
+fi