vfs: split followup tests into named test files

Replace the monolithic test-vfs-followups.js with individual test files:
- test-vfs-overlapping-mounts.js
- test-vfs-promises-open.js
- test-vfs-stream-properties.js
- test-vfs-dir-disposal.js
- test-vfs-stats-ino-dev.js
- test-vfs-append-write.js
- test-vfs-cross-device.js
- test-vfs-readdir-symlink-recursive.js
- test-vfs-package-json-cache.js
- test-vfs-readfile-async.js

Author: mcollina

test/parallel/test-vfs-append-write.js

@@ -0,0 +1,18 @@
+'use strict';
+
+// writeSync in append mode must append, not overwrite.
+
+require('../common');
+const assert = require('assert');
+const vfs = require('node:vfs');
+
+const myVfs = vfs.create();
+myVfs.writeFileSync('/append.txt', 'init');
+
+const fd = myVfs.openSync('/append.txt', 'a');
+const buf = Buffer.from(' more');
+myVfs.writeSync(fd, buf, 0, buf.length);
+myVfs.closeSync(fd);
+
+const content = myVfs.readFileSync('/append.txt', 'utf8');
+assert.strictEqual(content, 'init more');

test/parallel/test-vfs-cross-device.js

@@ -0,0 +1,31 @@
+'use strict';
+
+// Cross-VFS rename, copyFile, and link must throw EXDEV.
+
+require('../common');
+const assert = require('assert');
+const fs = require('fs');
+const vfs = require('node:vfs');
+
+const vfs1 = vfs.create();
+vfs1.writeFileSync('/src.txt', 'data');
+vfs1.mount('/xdev_a');
+
+const vfs2 = vfs.create();
+vfs2.mkdirSync('/dest');
+vfs2.mount('/xdev_b');
+
+assert.throws(() => fs.renameSync('/xdev_a/src.txt', '/xdev_b/dest/src.txt'), {
+  code: 'EXDEV',
+});
+
+assert.throws(() => fs.copyFileSync('/xdev_a/src.txt', '/xdev_b/dest/src.txt'), {
+  code: 'EXDEV',
+});
+
+assert.throws(() => fs.linkSync('/xdev_a/src.txt', '/xdev_b/dest/link.txt'), {
+  code: 'EXDEV',
+});
+
+vfs2.unmount();
+vfs1.unmount();

test/parallel/test-vfs-dir-disposal.js

@@ -0,0 +1,30 @@
+'use strict';
+
+// VirtualDir must support Symbol.dispose and Symbol.asyncDispose.
+
+const common = require('../common');
+const assert = require('assert');
+const fs = require('fs');
+const vfs = require('node:vfs');
+
+const myVfs = vfs.create();
+myVfs.mkdirSync('/dir');
+myVfs.writeFileSync('/dir/a.txt', 'a');
+myVfs.mount('/mnt_dirdispose');
+
+// Symbol.dispose via closeSync
+{
+  const dir = fs.opendirSync('/mnt_dirdispose/dir');
+  dir[Symbol.dispose]();
+  assert.throws(() => dir.closeSync(), { code: 'ERR_DIR_CLOSED' });
+}
+
+// Symbol.asyncDispose via close
+{
+  const dir = fs.opendirSync('/mnt_dirdispose/dir');
+  dir[Symbol.asyncDispose]().then(common.mustCall(() => {
+    assert.throws(() => dir.closeSync(), { code: 'ERR_DIR_CLOSED' });
+  }));
+}
+
+myVfs.unmount();

test/parallel/test-vfs-followups.js

@@ -0,0 +1,43 @@
+'use strict';
+
+// Overlapping VFS mounts must be rejected.
+
+require('../common');
+const assert = require('assert');
+const vfs = require('node:vfs');
+
+const vfs1 = vfs.create();
+vfs1.writeFileSync('/a.txt', 'a');
+vfs1.mount('/overlap_base');
+
+// Child of existing mount
+{
+  const v = vfs.create();
+  v.writeFileSync('/b.txt', 'b');
+  assert.throws(() => v.mount('/overlap_base/sub'), {
+    code: 'ERR_INVALID_STATE',
+    message: /overlaps/,
+  });
+}
+
+// Parent of existing mount
+{
+  const v = vfs.create();
+  v.writeFileSync('/b.txt', 'b');
+  assert.throws(() => v.mount('/overlap'), {
+    code: 'ERR_INVALID_STATE',
+    message: /overlaps/,
+  });
+}
+
+// Exact same mount point
+{
+  const v = vfs.create();
+  v.writeFileSync('/b.txt', 'b');
+  assert.throws(() => v.mount('/overlap_base'), {
+    code: 'ERR_INVALID_STATE',
+    message: /overlaps/,
+  });
+}
+
+vfs1.unmount();