test(ext/node): port _fs tests from std/node (#18262)

Co-authored-by: Yoshiya Hinosawa <stibium121@gmail.com>

cli/tests/unit_node/_test_utils.ts

@@ -0,0 +1,43 @@
+// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
+
+import {
+  assert,
+  assertStringIncludes,
+} from "../../../test_util/std/testing/asserts.ts";
+
+/** Asserts that an error thrown in a callback will not be wrongly caught. */
+export async function assertCallbackErrorUncaught(
+  { prelude, invocation, cleanup }: {
+    /** Any code which needs to run before the actual invocation (notably, any import statements). */
+    prelude?: string;
+    /**
+     * The start of the invocation of the function, e.g. `open("foo.txt", `.
+     * The callback will be added after it.
+     */
+    invocation: string;
+    /** Called after the subprocess is finished but before running the assertions, e.g. to clean up created files. */
+    cleanup?: () => Promise<void> | void;
+  },
+) {
+  // Since the error has to be uncaught, and that will kill the Deno process,
+  // the only way to test this is to spawn a subprocess.
+  const p = new Deno.Command(Deno.execPath(), {
+    args: [
+      "eval",
+      "--unstable",
+      `${prelude ?? ""}
+  
+        ${invocation}(err) => {
+          // If the bug is present and the callback is called again with an error,
+          // don't throw another error, so if the subprocess fails we know it had the correct behaviour.
+          if (!err) throw new Error("success");
+        });`,
+    ],
+    stderr: "piped",
+  });
+  const { stderr, success } = await p.output();
+  const error = new TextDecoder().decode(stderr);
+  await cleanup?.();
+  assert(!success);
+  assertStringIncludes(error, "Error: success");
+}