test: add test for Module._stat

Module._stat landed in #44537 without
a test, so this change adds one.

Signed-off-by: Darshan Sen <raisinten@gmail.com>
PR-URL: #44713
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Geoffrey Booth <webadmin@geoffreybooth.com>

test/parallel/test-module-stat.js

@@ -0,0 +1,25 @@
+'use strict';
+require('../common');
+
+// This tests Module._stat.
+
+const Module = require('module');
+const fs = require('fs');
+const tmpdir = require('../common/tmpdir');
+const { ok, strictEqual } = require('assert');
+const { join } = require('path');
+
+const directory = join(tmpdir.path, 'directory');
+const doesNotExist = join(tmpdir.path, 'does-not-exist');
+const file = join(tmpdir.path, 'file.js');
+
+tmpdir.refresh();
+fs.writeFileSync(file, "module.exports = { a: 'b' }");
+fs.mkdirSync(directory);
+
+strictEqual(Module._stat(directory), 1); // Returns 1 for directories.
+strictEqual(Module._stat(file), 0); // Returns 0 for files.
+ok(Module._stat(doesNotExist) < 0); // Returns a negative integer for any other kind of strings.
+
+// TODO(RaisinTen): Add tests that make sure that Module._stat() does not crash when called
+// with a non-string data type. It crashes currently.

test/parallel/test-vfs.js

@@ -0,0 +1,88 @@
+'use strict';
+const common = require('../common');
+
+// This tests the creation of a vfs by monkey-patching fs and Module._stat.
+
+const Module = require('module');
+const fs = require('fs');
+const tmpdir = require('../common/tmpdir');
+const { deepStrictEqual, ok, strictEqual, throws } = require('assert');
+const { join } = require('path');
+
+const directory = join(tmpdir.path, 'directory');
+const doesNotExist = join(tmpdir.path, 'does-not-exist');
+const file = join(tmpdir.path, 'file.js');
+
+tmpdir.refresh();
+fs.writeFileSync(file, "module.exports = { a: 'b' }");
+fs.mkdirSync(directory);
+
+strictEqual(Module._stat(directory), 1);
+ok(Module._stat(doesNotExist) < 0);
+strictEqual(Module._stat(file), 0);
+
+const vfsDirectory = join(process.execPath, 'directory');
+const vfsDoesNotExist = join(process.execPath, 'does-not-exist');
+const vfsFile = join(process.execPath, 'file.js');
+
+ok(Module._stat(vfsDirectory) < 0);
+ok(Module._stat(vfsDoesNotExist) < 0);
+ok(Module._stat(vfsFile) < 0);
+
+deepStrictEqual(require(file), { a: 'b' });
+throws(() => require(vfsFile), { code: 'MODULE_NOT_FOUND' });
+
+common.expectWarning(
+  'ExperimentalWarning',
+  'Module._stat is an experimental feature. This feature could change at any time');
+
+process.on('warning', common.mustCall());
+
+const originalStat = Module._stat;
+Module._stat = function(filename) {
+  if (!filename.startsWith(process.execPath)) {
+    return originalStat(filename);
+  }
+
+  if (filename === process.execPath) {
+    return 1;
+  }
+
+  switch (filename) {
+    case vfsDirectory:
+      return 1;
+    case vfsDoesNotExist:
+      return -2;
+    case vfsFile:
+      return 0;
+  }
+};
+
+const originalReadFileSync = fs.readFileSync;
+// TODO(aduh95): We'd like to have a better way to achieve this without monkey-patching fs.
+fs.readFileSync = function readFileSync(pathArgument, options) {
+  if (!pathArgument.startsWith(process.execPath)) {
+    return originalReadFileSync.apply(this, arguments);
+  }
+  if (pathArgument === vfsFile) {
+    return "module.exports = { x: 'y' };";
+  }
+  throw new Error();
+};
+
+fs.realpathSync = function realpathSync(pathArgument, options) {
+  return pathArgument;
+};
+
+strictEqual(Module._stat(directory), 1);
+ok(Module._stat(doesNotExist) < 0);
+strictEqual(Module._stat(file), 0);
+
+strictEqual(Module._stat(vfsDirectory), 1);
+ok(Module._stat(vfsDoesNotExist) < 0);
+strictEqual(Module._stat(vfsFile), 0);
+
+strictEqual(Module._stat(process.execPath), 1);
+
+deepStrictEqual(require(file), { a: 'b' });
+deepStrictEqual(require(vfsFile), { x: 'y' });