Add recursive deadlock test

Refs: #7
PR-URL: #18

test.js

@@ -6,6 +6,7 @@ const tests = [
   'steps',
   'exclusive',
   'deadlock',
+  'recursive-deadlock',
   'thread-main',
 ];
 

test/recursive-deadlock.js

@@ -0,0 +1,30 @@
+'use strict';
+
+const assert = require('assert').strict;
+
+const { locks } = require('..');
+
+const TEST_TIMEOUT = 100;
+
+module.exports = async () =>
+  new Promise(resolve => {
+    let flag1 = false;
+    let flag2 = false;
+
+    (async () => {
+      await locks.request('E', async () => {
+        flag1 = true;
+        await locks.request('E', async () => {
+          flag2 = true;
+        });
+      });
+    })();
+
+    (async () => {
+      setTimeout(() => {
+        assert.strictEqual(flag1, true);
+        assert.strictEqual(flag2, false);
+        resolve();
+      }, TEST_TIMEOUT);
+    })();
+  });