✨ Add a simple test runner and move tests to subdirectory

test.sh

@@ -0,0 +1,24 @@
+#!/bin/sh
+set -e
+
+count_ok=0
+count_failed=0
+
+for test in tests/*.sh; do
+    echo "== $test"
+    $test && result=$? || result=$?
+
+    if [[ $result = 0 ]]; then
+        echo "✔"
+        count_ok=$((count_ok+1))
+    else
+        echo "❌"
+        count_failed=$((count_failed+1))
+    fi
+    echo
+done
+
+echo "$count_ok ok, $count_failed failed"
+if [[ $count_failed -gt 0 ]]; then
+    exit 1
+fi