fixup: add explicit test for GH 21918

Author: joaocgreis

test/parallel/test-preload.js

@@ -132,6 +132,26 @@ childProcess.exec(
   }
 );
 
+// test that preloading with a relative path works
+process.chdir(fixtures.fixturesDir);
+childProcess.exec(
+  `"${nodeBinary}" ${preloadOption(['./printA.js'])} "${fixtureB}"`,
+  common.mustCall(function(err, stdout, stderr) {
+    assert.ifError(err);
+    assert.strictEqual(stdout, 'A\nB\n');
+  })
+);
+if (common.isWindows) {
+  // https://github.com/nodejs/node/issues/21918
+  childProcess.exec(
+    `"${nodeBinary}" ${preloadOption(['.\\printA.js'])} "${fixtureB}"`,
+    common.mustCall(function(err, stdout, stderr) {
+      assert.ifError(err);
+      assert.strictEqual(stdout, 'A\nB\n');
+    })
+  );
+}
+
 // https://github.com/nodejs/node/issues/1691
 process.chdir(fixtures.fixturesDir);
 childProcess.exec(