add test script

test.sh

@@ -0,0 +1,52 @@
+#!/usr/bin/bash
+
+set -euo pipefail
+
+cd "$(dirname "${BASH_SOURCE[0]}")/2020"
+
+run_solution() {
+	if [ -d "$solution" ]; then
+		runfile=$solution/run.sh
+		[ -f "$runfile" ] || { echo "Error: $runfile not found"; exit 1; }
+		"$runfile" "$input"
+	else
+		case "$(basename "$solution")" in
+			*.hs)
+				runhaskell -icommon "$solution" < "$input"
+				;;
+			*.py)
+				python "$solution" < "$input"
+				;;
+			*)
+				echo "Error: Unknown solution type: $solution"
+				exit 1
+				;;
+		esac
+	fi
+}
+
+for day in day*; do
+	input=data/$day.input
+	expected=data/$day.expected
+	for solution in "$day"/*; do
+		echo -n "$solution... "
+		solution_output=$(mktemp)
+		trap "rm $solution_output" EXIT
+		run_solution "$solution" > "$solution_output"
+
+		if ! diff -u "$expected" "$solution_output"; then
+			echo FAIL
+			rv=$?
+			case "$rv" in
+				1)
+					exit 2
+					;;
+				*)
+					exit 1
+					;;
+			esac
+		else
+			echo ok
+		fi
+	done
+done