better mock obj validation

lib/mock.js

@@ -1,6 +1,11 @@
 const Module = require('module')
 const { isAbsolute } = require('path')
 
+const isPlainObject = obj => obj
+  && typeof obj === 'object'
+  && (Object.getPrototypeOf(obj) === null
+    || Object.getPrototypeOf(obj) === Object.prototype)
+
 class Mock {
   constructor(parentFilename, filename, mocks = {}) {
     this.filename = filename
@@ -14,7 +19,7 @@ class Mock {
       throw new TypeError('t.mock() first argument should be a string')
     }
 
-    if (typeof mocks !== 'object') {
+    if (!isPlainObject(mocks)) {
       throw new TypeError(`mocks should be a a key/value object in which keys
 are the same used in ${filename} require calls`)
     }

test/mock.js

@@ -9,13 +9,43 @@ t.throws(
 )
 
 t.throws(
-  () => Mock.get(resolve(__filename)),
+  () => Mock.get(__filename),
   /first argument should be a string/,
   'should throw on invalid filename',
 )
 
 t.throws(
-  () => Mock.get(resolve(__filename), './foo.js', ''),
+  () => Mock.get(__filename, './foo.js', ''),
+  /mocks should be a a key\/value object in which keys/,
+  'should throw on invalid mock-defining object',
+)
+
+t.throws(
+  () => Mock.get(__filename, './foo.js', [1]),
+  /mocks should be a a key\/value object in which keys/,
+  'should throw on invalid mock-defining object',
+)
+
+t.throws(
+  () => Mock.get(__filename, './foo.js', null),
+  /mocks should be a a key\/value object in which keys/,
+  'should throw on invalid mock-defining object',
+)
+
+t.throws(
+  () => Mock.get(__filename, './foo.js', /foo/),
+  /mocks should be a a key\/value object in which keys/,
+  'should throw on invalid mock-defining object',
+)
+
+t.throws(
+  () => Mock.get(__filename, './foo.js', 1),
+  /mocks should be a a key\/value object in which keys/,
+  'should throw on invalid mock-defining object',
+)
+
+t.throws(
+  () => Mock.get(__filename, './foo.js', new Map()),
   /mocks should be a a key\/value object in which keys/,
   'should throw on invalid mock-defining object',
 )

test/test.js

@@ -1517,5 +1517,31 @@ t.test('require defining mocks', t => {
     )
   })
 
+  t.test('should support mocking builtin modules within nested deps', t => {
+    const f = t.testdir({
+      lib: {
+        'a.js':
+          `module.exports = require('./b.js')`,
+        'b.js':
+          `module.exports = require('./c.js')`,
+        'c.js':
+          `module.exports = () => require('fs')`,
+      },
+      'test.js':
+        `const t = require('../..'); // tap
+        t.test('mocking builtin modules in nested modules', t => {
+          const fs = {}
+          const a = t.mock('./lib/a.js', { fs })
+          t.equal(a(), fs, 'should get mocked fs result')
+          t.end()
+        })`,
+    })
+    return t.spawn(
+      process.execPath,
+      [ path.resolve(f, 'test.js') ],
+      { cwd: f },
+    )
+  })
+
   t.end()
 })